Gas properties — temperature effect on thermal conductivity of air Evaluate the statement: “Thermal conductivity of air increases with rise in temperature.”

Introduction / Context:
Thermal conductivity, k, indicates a substance’s ability to conduct heat by molecular transport. In gases, k is strongly tied to molecular motion and collision dynamics, which change with temperature.

Given Data / Assumptions:

• Ideal gas behavior approximation for air over common engineering ranges.
• No phase change; composition approximately constant.

Concept / Approach:
For gases, as temperature rises, molecular speeds increase and mean free path changes such that energy is transferred more rapidly between molecules. Kinetic theory therefore predicts an increase in thermal conductivity with temperature for most gases at low to moderate pressures, including air.

Step-by-Step Solution:
Consider kinetic theory: k ∝ c_p * density * molecular speed * mean free path factors.With temperature up, average molecular speed rises, increasing k.Empirical property tables for air confirm k increases from near 0.024 W/m·K at ~300 K to higher values at elevated temperatures.

Verification / Alternative check:
Heat transfer handbooks show monotonic increase of air’s thermal conductivity with T at atmospheric pressure across typical engineering temperatures.

Why Other Options Are Wrong:
(b) contradicts data. (c) and (d) impose arbitrary thresholds that are not fundamental. (e) While property charts often tabulate at 1 atm, the trend with temperature is not restricted to “constant pressure only.”

Common Pitfalls:
Confusing gas behavior with liquids; many liquids show decreasing k with temperature, opposite to gases like air.

Final Answer:
Correct