Which of the following has the least thermal conductivity?
A
air
B
ash
C
glass
D
water
Verified Correct Answer: A.
Physical Principles & Numerical Solution
Answer: A. air
(Air is a poor conductor ~0.025 W/mK; water ~0.6, glass ~1, ash varies but is higher.)
Air is a poor conductor of heat compared to solids and liquids like ash, glass, and water, making it a good insulator.
Source: Myschool Past Questions Archive (Record #74368)