For heat to flow from one end to the other in a solid,it is necessary to have:

For water at $0^{\circ} C$,it takes one hour for the first $3 \ mm$ of ice layer formation. How many hours will it take for the next $6 \ mm$ of ice formation?

Assertion: $A$ thermos bottle consists of a double-walled glass vessel with the space between the two walls evacuated,so that the heat transfer between the contents of the bottle and the outside is minimized.
Reason: The vacuum between the two walls inhibits the heat transfer by the radiation mechanism.
Which of the following is correct?

When two ends of a rod wrapped with cotton are maintained at different temperatures and after some time every point of the rod attains a constant temperature,then

Snow is more heat insulating than ice,because

Four rods of silver,copper,brass,and wood are of the same shape. They are heated together after wrapping a paper on each. The paper will burn first on: