An a-particle contains
(a) 4 positive charge and 2 mass unit
(b) 2 positive charge and 4 mass unit
(c) 2 positive charge and 2 mass unit
(d) 4 positive charges and 4 mass units.

Correct: (b) 2 positive charge and 4 mass unit

Explanation: Alpha particle is identical to the nucleus of the helium-4 atom, consisting of two protons and two neutrons bound together. Thus it has a mass of four units and a positive charge of two.