Question

if mass of the substance is 20g, then the heat energy required to melt 1 g of the substance is​

Answer 1

The substance melts by absorbing 340-40=300J of energy.i.e 20 g of substance absorbs 300 J of energy and melts.

Unit mass (1g) of substance absorbs 300/20=15J of energy and melts without rise in temperature.