Question

calculate the energy that can be obtained from complete annihilation of 1g of mass

Answer 1

This is an easy one once you know this famous equation of Einstein

E=mc^2

in your case m=0.001 kg c= 3 * 10^8 (always)

E= 0.001 * (3 *10^8)^2

E=0.001 * 9 * 10^16

E= 9 * 10^13 Joules