The specific heat of a metal is 0.5 cal/ (0c. g). the heat required to raise temperature of 100 gram of that metal by 20 0c is

The specific heat of the metal is 0.5 cal/ (0C.g). This means the energy needed is 0.5 cal to raise the heat of 1 gram of metal by 1 degree C. Therefore, the energy needed to raise 100 g of the metal by 20 degrees C is:
0.5 * 20 * 100 = 1000 cal.