Question

Metal M has a low melting point and is used as a coolant in nuclear reactor. then what is the M metal?

Answer 1

Given the properties, the metal is most probably Sodium.

Sodium has a low melting point of 97°C and its molten form is used as a coolant in nuclear reactors. 

Answer 2

Metal M is Sodium (Na)

Sodium has low melting point that is 98°C (approx)

It is also used as coolant in nuclear reactors to slow down the excited neutrons produced in a nuclear fission