A metal rod is heated to a temperature of $200 °\mathrm{C}$. It is placed in a room at $30 °\mathrm{C}$. At which temperature, the rod will stop radiating heat?

Give reason for the following:

The metal knob feels colder than the wooden knob at the same temperature.

Give reason for the following:

The appearance of fuel tank is usually shiny and smooth.

Give reason for the following:

A hot air balloon rises up in the sky. 

Give reason for the following:

The water pipe in a solar water heater is bent into the shape as given in the picture.