Question 1

Solutions (solubility): Which of the following substances is the most soluble in water at room temperature? Compare typical solubilities of common salts. Choose the correct substance.

Accepted Answer

Given data Ask: Most water-soluble substance among common salts. Concept/Approach At ~20–25 °C, ammonium nitrate has an exceptionally high solubility (well over 100 g per 100 g water), higher than KNO3 (~30–35 g/100 g water) and NaCl (~36 g/100 g water). CaCO3 is sparingly soluble. Final Answer Ammonium nitrate (NH₄NO₃)

Question 2

Solar spectroscopy (history of discovery): Which element was first discovered in the Sun’s chromosphere before being found on Earth? Identify the element detected during the 1868 total solar eclipse via a new spectral line. Choose the correct elemen…

Accepted Answer

What is being asked? Which element was first identified in the Sun's chromosphere (not on Earth) through spectroscopy. Given data Context: Solar chromosphere, 19th-century spectroscopy Clue: Discovered during the 1868 eclipse via an unknown yellow spectral line (D3) Concept/Approach A previously unknown line observed by Janssen and Lockyer was attributed to a new element, later named helium (from Helios, Sun). Helium was isolated on Earth only later. Step-by-step reasoning 1) Spectral line D3 in the yellow region did not match known elements.2) The element producing it was named helium.3) Therefore, the first element discovered in the Sun's chromosphere was helium. Common pitfalls Choosing hydrogen or neon; both were already known on Earth and are not the chromosphere-first discovery. Final Answer Helium

Question 3

Everyday chemistry: Soda water contains which dissolved gas under pressure? Focus on the fizzy constituent responsible for effervescence and tangy taste. Choose the correct gas.

Accepted Answer

What is being asked? The gas dissolved in soda water that produces bubbles and mild acidity. Given data Product: Soda water / carbonated water Concept/Approach Soda water is water into which CO2 is dissolved under pressure, forming carbonic acid (H2CO3) responsible for its tang. Final Answer Carbon dioxide

Question 4

Atomic structure (hydrogen): Which of the following is NOT an isotope of hydrogen? Recall the three isotopes of hydrogen and identify the odd one out. Choose the correct option.

Accepted Answer

What is being asked? Pick the option that is not a hydrogen isotope. Given data Hydrogen isotopes: protium (¹H), deuterium (²H or D), tritium (³H or T) Concept/Approach Hydronium is a polyatomic ion (H3O+) formed when H+ associates with water; it is not an isotope (same element with different mass numbers). Final Answer Hydronium (H3O+)

Question 5

Materials used in pencils: The writing core of ordinary pencils is made of which substance? Consider the soft, electrically conductive carbon form used for marking on paper. Choose the correct material.

Accepted Answer

What is being asked? The material that forms the pencil 'lead'. Given data Pencils use a carbon form mixed with clay (no metallic lead). Concept/Approach The pencil core is graphite (sp2 carbon) blended with clay and waxes; charcoal is too friable, silicon and phosphorus are not used. Final Answer Graphite

Question 6

Bioinorganic chemistry: Chlorophyll is a naturally occurring chelate in which the central metal ion is what? Identify the metal coordinated in the porphyrin-like ring of plant chlorophyll. Choose the correct metal.

Accepted Answer

What is being asked? The central metal in the chlorophyll macrocycle. Given data Chlorophyll is a chelate (chlorin ring analogous to porphyrin) Concept/Approach In chlorophyll a/b, the macrocycle chelates magnesium (Mg2+). (By contrast, heme contains Fe, and plastocyanin contains Cu.) Final Answer Magnesium (Mg)

Question 7

Elemental classification: Bromine is best described as which of the following at room temperature? Consider both physical state and its classification in the periodic table. Choose the correct description.

Accepted Answer

What is being asked? The physical state and class of bromine at room temperature. Given data Element group: Halogens (Group 17) Concept/Approach Bromine (Br2) is a reddish-brown liquid non-metal at room temperature; among elements, only bromine and mercury are liquids near 25 °C (mercury is a metal). Final Answer A non-metallic liquid (halogen)

Question 8

Physical chemistry (water types): Heavy water is chemically what? Identify the correct formula/name used in nuclear reactors as a moderator. Choose the correct compound.

Accepted Answer

What is being asked? The chemical identity of heavy water. Given data Use: Neutron moderator in some reactors Concept/Approach Heavy water is deuterium oxide (D2O), where hydrogen is replaced by its isotope deuterium (²H). Final Answer Deuterium oxide (D2O)

Question 9

Water treatment (hardness): Permanent hardness of water can be removed by adding which chemical? Target the sulfate/chloride salts of Ca/Mg (non-carbonate hardness). Choose the correct reagent.

Accepted Answer

What is being asked? The reagent that removes permanent hardness (Ca/Mg chlorides/sulfates) by precipitation. Given data Permanent hardness ≠ carbonate hardness Concept/Approach Na2CO3 reacts with Ca2+/Mg2+ to form insoluble carbonates (CaCO3, MgCO3), thus softening the water. Lime mainly addresses temporary hardness by precipitating carbonates from bicarbonates. Final Answer Washing soda (sodium carbonate, Na2CO3)

Question 10

Allotropy of carbon: Carbon, diamond, and graphite are collectively referred to as what? Identify the term for different structural forms of the same element. Choose the correct term.

Accepted Answer

What is being asked? The common term for distinct structural forms of the same element. Given data Element: Carbon; forms: diamond (sp3), graphite (sp2), amorphous carbon Concept/Approach Different bonding/structure of the same element are called allotropes; isomers apply to compounds, isotopes to nuclei with different neutron counts, isobars to nuclides with the same mass number. Final Answer Allotropes

Question 11

Corrosion/tarnish of alloys: Brass gets discoloured in air due to the presence of which gas? Identify the gas that reacts with copper in brass to form a dark sulfide film. Choose the correct gas.

Accepted Answer

What is being asked? The atmospheric gas responsible for the dark tarnish on brass. Given data Alloy: Brass (Cu + Zn) Concept/Approach H2S in air reacts with copper to form copper sulfide films, causing discoloration; oxygen alone forms oxide patina more slowly, while CO2 and N2 are largely inert here. Final Answer Hydrogen sulfide (H2S)

Question 12

Everyday science (gases): Identify the gas commonly used to fill party/science balloons. Balloons require a gas that is lighter than air and non-flammable for safety. Choose the correct gas.

Accepted Answer

Given data Balloons need a lift-giving gas that is safe. Options include inert and reactive gases. Concept/Approach Lift requires a gas less dense than air. Helium is lighter than air and inert (non-flammable), making it the standard choice for balloons. Hydrogen is lighter but flammable—therefore unsafe for general use. Reasoning • Air density ≈ 1.225 kg/m³ (at STP); helium ≈ 0.178 kg/m³ → provides buoyancy. • Nitrogen/oxygen/argon are close to or heavier than air; they do not provide useful lift. Final Answer Helium

Question 13

Physical chemistry (solvation): Why is water a particularly good solvent for ionic salts? Base your choice on the molecular property of H₂O that stabilizes ions in solution. Choose the correct reason.

Accepted Answer

Given data Property of water that explains dissolution of ionic solids. Concept/Approach Water is a highly polar molecule with a large dipole moment. This strong polarity creates ion–dipole interactions that stabilize separated cations and anions, lowering the free energy of dissolution. Step-by-step reasoning • Ionic crystal → ions held by lattice energy. • In water, ion–dipole attractions (Hδ⁺ to anions, Oδ⁻ to cations) hydrate the ions. • Hydration energy counteracts lattice energy → salt dissolves. Final Answer It has a high dipole moment

Question 14

Inorganic chemistry (periodic table): The metals Fe, Co, and Ni are best classified as what? Consider their d-block character and typical properties. Choose the correct classification.

Accepted Answer

Given data Elements: Fe, Co, Ni (atomic numbers 26, 27, 28). Concept/Approach These are d-block elements with partially filled d-subshells in common oxidation states, fitting the definition of transition metals. Final Answer Transition metals

Question 15

Allotropes of carbon: Identify the hardest and the softest allotrope among the given pairs. Use known mechanical properties of carbon forms (sp³ vs sp²/amorphous). Choose the correct pair.

Accepted Answer

Given data Compare carbon allotropes for hardness. Concept/Approach Diamond (3D sp³ network) has extremely strong covalent bonds → highest hardness. Graphite has layered sp² sheets with weak interlayer forces → very soft and lubricating. Final Answer Diamond is the hardest; graphite is the softest

Question 16

Metals at room temperature: Which metal is liquid at ordinary room temperature (~25 °C)? Select the standard example used in science and daily life. Choose the correct metal.

Accepted Answer

Given data Ask: Metal that is liquid at ~25 °C. Concept/Approach Mercury (Hg) has a melting point of −38.83 °C and remains liquid at room temperature. (Gallium melts near 29.8 °C, so it can be solid at cooler room conditions; alkali/rare-earth options listed are solids at 25 °C.) Final Answer Mercury

Question 17

Basic classification (matter): Air is best described as which of the following? Consider composition (N₂, O₂, Ar, CO₂, etc.) and bonding. Choose the correct classification.

Accepted Answer

Given data Air contains multiple gases in variable proportions. Concept/Approach Because air is a physical combination of gases without fixed composition or chemical bonding between them, it is a mixture, not a single compound or element. Final Answer Mixture

Question 18

Metallurgy (amalgams): Which metal characteristically forms amalgams with many other metals? Think of liquid-metal solutions used in dentistry/electrochemistry. Choose the correct metal.

Accepted Answer

Given data Amalgam definition: an alloy containing mercury. Concept/Approach Mercury forms amalgams with many metals (e.g., Ag, Au, Zn, Sn). Thus, the metal that forms amalgams with others is mercury. Final Answer Mercury

Question 19

Minerals and elements: Radium is obtained from which ore/mineral? Recall its historical extraction source alongside uranium. Choose the correct mineral.

Accepted Answer

Given data Element: Radium (Ra). Concept/Approach Radium occurs as a trace decay product in uranium ores, especially pitchblende (uraninite). Curie's original isolation was from pitchblende residues. Final Answer Pitchblende (uraninite)

Question 20

Alloys (copper-based): Which metals constitute gunmetal (traditional composition)? Think of the bronze used historically for guns/valves/bearings. Choose the correct ingredient set.

Accepted Answer

Given data Alloy: Gunmetal (a bronze). Concept/Approach Traditional gunmetal is a copper–tin bronze (often with a small percentage of zinc/lead in modern specs). Among the options given, the correct core constituents are copper and tin. Final Answer Copper, Tin

General Science Questions