An alpha particle is also referred to as a nucleus of which isotope?

The correct answer is helium 4.

Explanation:

A positively charged particle, which comprises two protons and two neutrons is called an alpha particle. There is a similarity between the alpha particle and a helium atom as helium atom also possess mass number, that is, no of protons plus no of neutrons as 4, and atomic number, that is, number of protons a 2.  

Therefore, it can be said that an alpha particle is also considered as a nucleus of helium isotope.  

c. is the correct answer