Thermal diffusivity comparison: identify the material with the highest α = k/(ρ·cᵖ). Options: iron, lead, concrete, and wood. Select the material that typically exhibits the greatest thermal diffusivity in engineering data. Choose the correct option.

Given data and idea
Thermal diffusivity: α = k/(ρ·cᵖ) — how quickly a material's temperature equalizes internally.

Reasoning with typical properties
Iron (steel-like): k ≈ 50–80 W/m·K, ρ ≈ 7.9×10³ kg/m³, cᵖ ≈ 0.45 kJ/kg·K → α ≈ 2.0–2.5×10⁻⁵ m²/s.Lead: k ≈ 35 W/m·K, ρ ≈ 11.34×10³ kg/m³, cᵖ ≈ 0.128 kJ/kg·K → α ≈ 35/(11 340×128) ≈ 2.4×10⁻⁵ m²/s.Concrete and wood have much lower k and larger ρ·cᵖ, hence far smaller α (≈10⁻⁶ to 10⁻⁷ m²/s order).

Conclusion
Among the listed choices, lead generally exhibits the highest thermal diffusivity.