Answer: b) positron
Explanation:
The antiparticle or the antimatter counterpart of the electron is called positron.
The positron has an electric charge of +1 e and same mass as an electron. When a positron collides with an electron, annihilation takes place.
Below is an attachnent that further explains this
The mass is the total number of protons and neutrons there are in the nucleus. There are 15 and 18 neutrons, that means the mass is 33
15 + 18 = 33