Question

there is a metal grill at the back of a fridge why​

Answer 1

There is a metal grill behind the fridge for better heat transfer.It increases the surface area ,as a result heat transfer rate also increases.

Answer 2

Answer:

This metal grill that you're saying is called the condenser. It contains a liquid/gas called the 'refrigerant'. This gas comes from the freezer where it had taken heat from the contents of the freezer and evaporated in the process, now it is giving the heat to the environment and turning into a liquid.