If a liquid is heated in weightlessness,the heat is transmitted through

Define heat transfer in solids.

The bottom of a lake is at $0^{\circ} C$ and the atmospheric temperature is $-20^{\circ} C$. If $1 \, cm$ of ice is formed on the surface in $24 \, h$,then the time taken to form the next $1 \, cm$ of ice is ......... $h$.

What is heat transfer? Give its types.

What is thermal steady state?

What is temperature gradient? When is the temperature gradient considered positive and when is it considered negative?