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?

End $A$ of a copper rod is maintained in a steam chamber at $100\,^{\circ}C$ and the other end $B$ is maintained at $0\,^{\circ}C$. Assuming $x = 0$ at $A$,the $T-x$ graph in steady state will be:

The heat is flowing through a rod of length $50 \ cm$ and area of cross-section $5 \ cm^2$. Its ends are respectively at $25^\circ C$ and $125^\circ C$. The coefficient of thermal conductivity of the material of the rod is $0.092 \ kcal/m \cdot s \cdot ^\circ C$. The temperature gradient in the rod is

Under steady state,the temperature of a body

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

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?