Question

What is the mass number of an alpha particle?
(1) 1 (3) 0
(2) 2 (4) 4

Answer 1

(4) 4 is your answer because 4 is the mass number of an alpha particle. 

Answer 2

Your answer is (4) 4, because the alpha particle is a helium nucleus (either an ion or an ejected particle from alpha decay), and it has a mass number of 4, being consisted of four nucleons, (2 protons and 2 neutrons).