Question 1

Assertion–Reason (Thermometry):
Assertion (A): Alcohol, rather than mercury, is used in a thermometer to measure very low temperatures around –60 °C.
Reason (R): Alcohol has a much lower freezing point than mercury.

Accepted Answer

Introduction / Context: This Assertion–Reason problem tests conceptual understanding of thermometric liquids and why different fluids (alcohol vs mercury) are selected for different temperature ranges. The focus is on low-temperature measurement near –60 °C and how material properties drive instrument design. Given Data / Assumptions: Assertion: Alcohol (e.g., ethanol or dyed spirit) is preferred for thermometers at very low temperatures such as –60 °C. Reason: Alcohol freezes at a much lower temperature than mercury. Objective: Decide truth values and whether the reason explains the assertion. Concept / Approach: Thermometric liquids must remain liquid across the working range and expand sufficiently with temperature. Mercury solidifies at around –38.8 °C, so it cannot measure temperatures below that point. Common alcohols (ethanol) remain liquid well below –60 °C and possess a high coefficient of thermal expansion, yielding good sensitivity. Step-by-Step Solution: 1) Check A: At –60 °C mercury would be solid; thus alcohol thermometers are used. A is true.2) Check R: Alcohol has a far lower freezing point than mercury (ethanol ~ –114 °C), so R is true.3) Causality: The very reason alcohol does not freeze in that range is precisely why it is chosen. Hence R correctly explains A. Verification / Alternative check: Beyond freezing point, note ancillary factors: alcohol wets glass better and allows visibility via dye; mercury, though better for moderate ranges due to linearity and non-wetting behavior, is unusable when solidified. Why Other Options Are Wrong: “Both true but not explanation” ignores the direct causal link; “A true, R false” contradicts known freezing points; “A false…” is inconsistent with practice. Common Pitfalls: Confusing boiling point with freezing point; assuming mercury’s wide usability implies suitability at all temperatures. Final Answer: Both A and R are true, and R explains A.

Question 2

Assertion–Reason (Tides):
Assertion (A): Tides indicate the regular, periodic rise and fall of sea level.
Reason (R): Tides are caused by the gravitational pull of the Moon and sea level.

Accepted Answer

Introduction / Context: The item checks understanding of what tides are and their primary causes. It also probes careful reading because the Reason statement contains a subtle error in phrasing. Given Data / Assumptions: Assertion: Tides are regular periodic oscillations of sea level. Reason: Tides are caused by gravitational pull of the Moon and “sea level” (as written). Concept / Approach: Tides are generated mainly by the differential (tidal) gravitational forces of the Moon and the Sun acting on Earth’s oceans, modulated by Earth’s rotation and basin geometry. The Reason as stated improperly lists “sea level” instead of the Sun as a cause. Step-by-Step Solution: 1) A: Correct. Tides are periodic rises and falls of ocean levels.2) R: Incorrect as written. The correct causal agents are the Moon and the Sun (plus Earth–Moon system rotation), not “sea level.” Therefore R is false.3) Relation: Since A is true and R is false, option indicating “A true, R false” follows. Verification / Alternative check: If the Reason had said “Moon and the Sun,” it would be true and would explain A. The provided wording invalidates it. Why Other Options Are Wrong: Any option treating R as true ignores the explicit wording error; saying A is false contradicts standard definitions. Common Pitfalls: Skimming past the misprint and assuming the standard correct text. Final Answer: A is true but R is false.

Question 3

Assertion–Reason (Graphite Properties):
Assertion (A): Graphite is slippery and used as a lubricant.
Reason (R): Graphite has free (delocalized) electrons.

Accepted Answer

Introduction / Context: This question distinguishes between two different properties of graphite: lubricity (slipperiness) and electrical conduction. It asks whether the presence of delocalized electrons explains why graphite acts as a lubricant. Given Data / Assumptions: Graphite is observed to be slippery and is used industrially as a dry lubricant. Graphite’s bonding involves delocalized electrons in hexagonal carbon sheets. Concept / Approach: Graphite consists of layers (graphene sheets) held together by weak van der Waals forces. The ease with which these layers slide over one another provides lubricity. Delocalized electrons largely explain graphite’s ability to conduct electricity along the planes, not its slipperiness. Step-by-Step Solution: 1) A: True. The layered structure allows low shear resistance.2) R: True statement about electronic structure; graphite does possess delocalized electrons.3) Link: The explanation for lubricity is interlayer sliding due to weak interlayer bonding, not the presence of free electrons. Hence R does not explain A. Verification / Alternative check: Compare with diamond: no delocalized electrons, extremely hard, not slippery. The determining factor for slip is bonding anisotropy rather than electron delocalization. Why Other Options Are Wrong: “A & R true and explanatory” conflates conduction with lubrication; “A true, R false” denies correct electronic structure; “A false” contradicts common use. Common Pitfalls: Assuming one “special property” of graphite accounts for all behaviors. Final Answer: Both A and R are true, but R does not correctly explain A.

Question 4

Assertion–Reason (Deliquescence of Common Salt):
Assertion (A): When common salt is kept open, it absorbs moisture from the air.
Reason (R): Commercial common salt contains magnesium chloride (and similar impurities).

Accepted Answer

Introduction / Context: The problem targets understanding of hygroscopic/deliquescent behavior in household salt. It tests whether moisture uptake is intrinsic to pure NaCl or due to impurities commonly present in table salt. Given Data / Assumptions: Observation: “Common salt” kept open becomes moist. Claimed reason: Presence of magnesium chloride (and similar chlorides) in commercial salt. Concept / Approach: Pure sodium chloride is not strongly deliquescent at typical ambient conditions. However, impurities such as MgCl2 and CaCl2 are highly hygroscopic/deliquescent and readily absorb atmospheric moisture. In practice, commercial salts often contain traces of these chlorides, explaining the wetting effect. Conversely, “free-flow” table salts are treated with anti-caking agents to reduce clumping. Step-by-Step Solution: 1) A: True—everyday experience and chemistry labs note moistening/clumping in open salt containers.2) R: True—MgCl2/CaCl2 absorb moisture; even small amounts can draw in water.3) Explanation: The impurities’ deliquescence directly causes the observed moisture uptake. Thus R explains A. Verification / Alternative check: Observe that very pure NaCl under controlled humidity clumps far less. Anti-caking additives (e.g., sodium ferrocyanide in tiny amounts) further mitigate moisture effects. Why Other Options Are Wrong: Any option denying R’s explanatory role conflicts with well-known hygroscopic behavior of alkaline earth chlorides. Common Pitfalls: Attributing the behavior solely to NaCl; ignoring role of impurities and ambient humidity. Final Answer: Both A and R are true, and R explains A.

Question 5

Assertion–Reason (History of the Steam Engine):
Assertion (A): The steam engine was invented by James Watt.
Reason (R): There was a pressing problem of removing water from flooded mines.

Accepted Answer

Introduction / Context: This item checks historical accuracy about the steam engine’s origins and distinguishes between “invention” and “improvement.” It also references the real 18th-century industrial problem of pumping water from mines. Given Data / Assumptions: Assertion: James Watt invented the steam engine. Reason: Pumping floodwater from mines was a major problem needing technological solutions. Concept / Approach: Historically, Thomas Savery (1698) and Thomas Newcomen (early 1700s) created practical atmospheric/steam engines for pumping water from mines before James Watt. Watt (1760s–1770s) revolutionized efficiency by introducing the separate condenser and other enhancements, leading to widespread industrial adoption. Thus, saying Watt “invented” the steam engine is inaccurate; he significantly improved it. Step-by-Step Solution: 1) Evaluate A: Strictly false—Watt is not the original inventor, though common parlance credits him for transformative improvements.2) Evaluate R: True—drainage of mines drove early steam technology.3) Relation: A is false, R is true; the reason is historically correct but does not turn A to true. Verification / Alternative check: Compare timelines: Savery’s “fire engine” patent (1698), Newcomen atmospheric engines (from ~1712), Watt’s separate condenser patent (1769). Why Other Options Are Wrong: Treating A as true ignores pre-Watt pioneers; claiming R false denies the well-documented mining impetus. Common Pitfalls: Equating “made it efficient and popular” with “invented.” Final Answer: A is false but R is true.

Question 6

Assertion–Reason (Clothing & Heat):
Assertion (A): We prefer to wear white clothes in winter.
Reason (R): White clothes are good reflectors of heat (radiation).

Accepted Answer

Introduction / Context: This question probes everyday thermal reasoning about clothing color and radiative heat transfer in different seasons. Given Data / Assumptions: Assertion claims a winter preference for white clothes. Reason asserts that white reflects heat effectively. Concept / Approach: White surfaces reflect most incident radiation and absorb less; black/dark surfaces absorb more. In hot conditions (summer), white clothing reduces solar heat gain and feels cooler. In cold conditions (winter), people generally prefer darker colors to absorb available radiant heat, all else equal. Step-by-Step Solution: 1) A: Typically false—people tend to prefer dark colors in winter for warmth; white is commonly preferred in summer.2) R: True—white is a good reflector of radiation.3) Relation: R being true actually contradicts the supposed winter “preference” in A, reinforcing that A is false. Verification / Alternative check: Consider outdoor sunlight exposure: white garments reduce radiant heat absorption, beneficial in heat, not cold. Why Other Options Are Wrong: Any claim that A is true does not align with standard thermal behavior and common practice. Common Pitfalls: Overgeneralizing cultural dress codes irrespective of physics; ignoring that insulation, thickness, windproofing also matter but color trend remains. Final Answer: A is false but R is true.

Question 7

Assertion–Reason (Soil & Earthworms):
Assertion (A): Earthworms are not good for agriculture.
Reason (R): Earthworms break down soil into fine particles and make it soft.

Accepted Answer

Introduction / Context: This item concerns the role of earthworms in soil health and agricultural productivity. Given Data / Assumptions: A claims earthworms are not good for agriculture. R states earthworms fragment soil and loosen it. Concept / Approach: Earthworms are widely recognized as beneficial: they aerate soil, enhance drainage, fragment organic matter, improve aggregation, and promote nutrient cycling (castings enrich soil). Their burrowing increases porosity, helping roots and water infiltration. Step-by-Step Solution: 1) A: False. Agronomy regards earthworms as “farmer’s friends.”2) R: True. By feeding and burrowing, worms create fine, friable soil and improve tilth.3) Hence “A false, R true.” Verification / Alternative check: Observe vermicomposting and sustainable agriculture literature; earthworm activity correlates with improved soil structure and fertility. Why Other Options Are Wrong: Any option treating A as true contradicts mainstream agronomy. Common Pitfalls: Confusing earthworms with crop pests; overlooking context where excessive burrowing in very specific situations is a minor issue compared to overall benefits. Final Answer: A is false but R is true.

Question 8

Assertion–Reason (Planets):
Assertion (A): Mercury is the farthest planet from the Sun.
Reason (R): Mercury is the smallest planet in the solar system.

Accepted Answer

Introduction / Context: This basic astronomy item asks you to separate positional order from size ranking among planets. Given Data / Assumptions: Mercury’s orbital position and size are being compared. Concept / Approach: Mercury is the closest planet to the Sun, not the farthest. Neptune is the farthest among the eight recognized planets. Mercury, however, is indeed the smallest planet since Pluto’s reclassification as a dwarf planet. Step-by-Step Solution: 1) A: False—Mercury is innermost.2) R: True—Mercury is the smallest planet.3) Therefore: A false, R true. Verification / Alternative check: Planet order from Sun outward: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Why Other Options Are Wrong: Any answer claiming A true contradicts elementary planetary order; claiming R false ignores accepted planetary sizes. Common Pitfalls: Conflating “smallest” with “farthest” or misremembering Pluto’s historical status. Final Answer: A is false but R is true.

Question 9

Assertion–Reason (Genetics – Color Blindness):
Assertion (A): Red–green color blindness occurs more frequently in males than in females.
Reason (R): Females have two X chromosomes, whereas males have only one.

Accepted Answer

Introduction / Context: The question examines understanding of X-linked recessive inheritance using red–green color blindness as the classic example. Given Data / Assumptions: Trait occurs more in males. Chromosomal complement: males XY; females XX. Concept / Approach: In X-linked recessive traits, a single mutant allele on the X chromosome is sufficient to express the phenotype in males (XY). Females (XX) would need two mutant alleles to express the condition; with only one mutant allele they are typically carriers without full expression, reducing prevalence among females. Step-by-Step Solution: 1) A: True—statistically, males show higher incidence.2) R: True—chromosomal complement explains hemizygous exposure in males.3) The reason directly explains the observation in A. Verification / Alternative check: Pedigree patterns show affected males more frequently and transmission via carrier mothers; father-to-son transmission does not occur for X-linked traits. Why Other Options Are Wrong: They deny either the epidemiological pattern or the genetic mechanism. Common Pitfalls: Assuming dominance or autosomal inheritance; overlooking carrier females. Final Answer: Both A and R are true, and R explains A.

Question 10

Assertion–Reason (Indus Valley Civilization):
Assertion (A): Indus Valley people knew the art of navigation.
Reason (R): Indus seals and artifacts indicate the prevalence of overseas trade.

Accepted Answer

Introduction / Context: This item concerns archaeological inference: whether material evidence of long-distance trade supports knowledge of navigation among Indus Valley people. Given Data / Assumptions: Artifacts and seals imply trade links with Mesopotamia and other regions. Assertion claims knowledge of navigation. Concept / Approach: Evidence such as dockyards (Lothal), standardized weights, seals, and imported/exported materials points to organized commerce, likely including maritime trade. Maritime commerce, in turn, implies practical navigation knowledge sufficient for coastal voyages and possibly open-water segments. Step-by-Step Solution: 1) A: True—archaeological context supports practical navigation for trade.2) R: True—seals and port structures indicate overseas/commercial connectivity.3) R gives the evidentiary basis for A, so it explains the assertion. Verification / Alternative check: Lothal’s dock-like structure and trade records align with maritime activity, a proxy for navigation skills. Why Other Options Are Wrong: Denying either statement contradicts archaeological consensus; denying explanatory link ignores that overseas trade presupposes navigation competencies. Common Pitfalls: Overstating sophistication (e.g., celestial navigation) versus practical coastal navigation; the assertion requires only practical capability. Final Answer: Both A and R are true, and R explains A.

Question 11

Assertion–Reason (Blood Groups):
Assertion (A): A person with blood group O is called a universal donor.
Reason (R): Group O red blood cells do not carry A or B antigens.

Accepted Answer

Introduction / Context: The question reviews ABO blood grouping concepts and the rationale behind the term “universal donor.” Given Data / Assumptions: Group O means absence of A and B antigens on RBC surfaces. Discussion is within the simplified school context (neglecting Rh for brevity). Concept / Approach: Transfusion reactions arise when recipient antibodies bind to donor RBC antigens. Since group O lacks A/B antigens, the chance of an ABO incompatibility reaction for red cell transfusion is minimal, which is why O (particularly O negative) is termed “universal donor” in simplified treatments. Step-by-Step Solution: 1) A: True in simplified/educational context (strictly, O negative is universal for packed RBCs).2) R: True—absence of A/B antigens underlies reduced risk of agglutination.3) R explains A because it cites the immunohematological basis. Verification / Alternative check: Real-world practice also considers the Rh factor and component transfusion protocols; nevertheless, the pedagogical principle holds. Why Other Options Are Wrong: Calling R false contradicts ABO fundamentals; calling A false ignores conventional terminology used in exams. Common Pitfalls: Confusing plasma transfusion rules (AB is plasma universal donor) with RBC transfusion. Final Answer: Both A and R are true, and R explains A.

Question 12

Assertion–Reason (Rivers of the Himalaya):
Assertion (A): Most Himalayan rivers are perennial.
Reason (R): They are fed by melting snow.

Accepted Answer

Introduction / Context: This geography question examines why Himalayan rivers maintain flow year-round. Given Data / Assumptions: Perennial means flowing throughout the year. Reason attributes base supply to melting snow/ice. Concept / Approach: Himalayan rivers (e.g., Ganga, Indus, Brahmaputra tributaries) originate in high-altitude snowfields and glaciers. Seasonal meltwater, combined with monsoon rainfall, sustains discharge even outside rainy months, making them perennial. Peninsular rivers, by contrast, are more rain-fed and can be seasonal in stretches. Step-by-Step Solution: 1) A: True—major Himalayan rivers flow year-round.2) R: True—glacial and snow melt provide sustained baseflow.3) R explains A: the melt source underpins perennial character. Verification / Alternative check: Hydrographs of snow/glacier-fed rivers show significant dry-season baseflow compared to purely rain-fed rivers. Why Other Options Are Wrong: They deny well-established hydrology. Common Pitfalls: Overgeneralizing to all Indian rivers or ignoring monsoon contributions. Final Answer: Both A and R are true, and R explains A.

Question 13

Assertion–Reason (Buoyancy & Densities):
Assertion (A): An iron ball floats on mercury but sinks in water.
Reason (R): The specific gravity (density) of iron is greater than that of mercury.

Accepted Answer

Introduction / Context: This physics item tests Archimedes’ principle and relative densities to predict floating/sinking behavior. Given Data / Assumptions: Iron density ~7.8 g/cm^3. Water density ~1.0 g/cm^3 (at ~4 °C). Mercury density ~13.6 g/cm^3. Concept / Approach: A body floats if its average density is less than the fluid’s or if the buoyant force can balance weight before full submergence. Iron is denser than water, so it sinks in water. Mercury is much denser than iron; an iron ball displaces enough mercury to balance its weight before submerging fully, hence it floats. Step-by-Step Solution: 1) A: True—empirically, iron sinks in water and floats on mercury.2) R: False—the statement says iron is denser than mercury; in fact, mercury is denser than iron. That is why iron floats on it.3) Therefore, “A true, R false.” Verification / Alternative check: Compute relative densities: 7.8 < 13.6 confirms float on mercury. Why Other Options Are Wrong: Any option that accepts R as true contradicts well-known densities. Common Pitfalls: Reversing which material has greater density. Final Answer: A is true but R is false.

Question 14

Assertion–Reason (Noise Pollution):
Assertion (A): Noise pollution is the unwanted accumulation of sound (noise) in the environment.
Reason (R): Noise pollution interferes with communication.

Accepted Answer

Introduction / Context: The question checks recognition of a core effect that makes environmental noise a pollutant. Given Data / Assumptions: Noise pollution involves undesirable, intrusive sound. One major consequence is communication interference (masking speech, alarms). Concept / Approach: Noise becomes a pollutant when it negatively affects health, comfort, productivity, wildlife behavior, and crucially, intelligible communication. Masking of speech and signals is a principal adverse effect, directly connecting the definition to its harmful impact. Step-by-Step Solution: 1) A: True—defines noise pollution as unwanted/intrusive sound accumulation.2) R: True—communication masking is a key harm attributable to noise.3) The reason articulates a principal mechanism that makes such sound “pollution,” so it explains A. Verification / Alternative check: Standards for noise levels (dB limits) often derive from speech intelligibility, sleep disturbance, and health endpoints; communication impairment is central. Why Other Options Are Wrong: They either deny a correct definition or ignore a canonical consequence. Common Pitfalls: Thinking only “loudness” matters; duration, frequency content, and context also determine interference. Final Answer: Both A and R are true, and R explains A.

Question 15

Assertion–Reason (Mughal History):
Assertion (A): Akbar founded Din-i Ilahi.
Reason (R): He was motivated purely by self-glorification.

Accepted Answer

Introduction / Context: This history item asks you to separate a factual act (founding Din-i Ilahi) from a subjective claim about motive. Given Data / Assumptions: Akbar instituted Din-i Ilahi (Divine Faith) in the late 16th century. Reason alleges self-glorification as the motive. Concept / Approach: Din-i Ilahi blended selected elements from multiple religions to promote tolerance and imperial cohesion. While interpretations of Akbar’s motives vary, mainstream accounts emphasize syncretism, political consolidation, and social harmony rather than mere self-glorification. Therefore, the factual assertion is correct, but the stated motive is oversimplified and inaccurate. Step-by-Step Solution: 1) A: True—Akbar founded Din-i Ilahi.2) R: False as a definitive motive; historical analyses present broader aims (sulh-i kul, administrative unity).3) Thus: A true, R false. Verification / Alternative check: Review Akbar’s policies: abolition of jizya (temporarily), debates in Ibadat Khana, inclusion of diverse nobles—consistent with tolerance aims. Why Other Options Are Wrong: They either deny the well-known founding or accept an unjustified singular motive. Common Pitfalls: Ascribing complex statecraft to a single emotive driver. Final Answer: A is true but R is false.

Question 16

Assertion–Reason (Nobel Prize – Economics):
Assertion (A): Amartya Sen was awarded the Nobel Prize in Economic Sciences.
Reason (R): He made invaluable contributions to developmental economics and welfare theory.

Accepted Answer

Introduction / Context: This item checks factual recognition of the Nobel Prize and understanding of why it was conferred. Given Data / Assumptions: Amartya Sen received the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel (commonly called the Nobel Prize in Economics). His work spans welfare economics, social choice, poverty and famine analysis, and development. Concept / Approach: Sen’s seminal contributions include capability approach, analysis of famines (entitlement theory), and advances in social choice theory extending Arrow’s work. These contributions profoundly influenced developmental economics and policy evaluation—directly underpinning the award. Step-by-Step Solution: 1) A: True—he is a recognized laureate.2) R: True—his influential, field-shaping contributions in development and welfare provide the rationale.3) Therefore, R explains A. Verification / Alternative check: His writings (e.g., “Poverty and Famines,” capability framework with Martha Nussbaum’s related work) are pillars in development studies. Why Other Options Are Wrong: They either deny the award or disconnect it from the substance of his contributions. Common Pitfalls: Confusing Peace Prize recipients or misattributing reasons (e.g., macroeconomic policy) unrelated to his core scholarship. Final Answer: Both A and R are true, and R explains A.

Question 17

Assertion (A) The world bank is a leading International Financial Institution. Reason (R) Ever, since its formation, it has played a major role in disbursing aid and support to economies across the world.

Accepted Answer

Both A and R are true and because of the reason the assertion is true.

Question 18

Assertion (A) In the Indian democratic system, the cabinet ministers are appointed by the President. Reason (R) The Prime Minister plays an advisory role.

Accepted Answer

Both A and R are true but R is not the reason for A.

Question 19

Assertion (A) India is a country of diverse cultures, customs and languages. Reason (R) What we now call India is the modern version of Bharat.

Accepted Answer

Both A and R are true but R is not the reason for A.

Question 20

Assertion (A) The ozone layer present in the upper atmosphere of Earth is beneficial for sustaining life on the Earth. Reason (R) The ozone layer blocks the harmful ultraviolet rays from the Sun and thus proctects life on the Earth.

Accepted Answer

Both A and R are true and R is the reason for A.

Assertion and Reason Questions