An alpha particle is:
a hydrogen atom
a nucleus of helium
two neutrons
an electron

a nucleus of helium

Explanation:

An alpha particle is a positively charged nucleus of a HELIUM-4 atom (consisting of two protons and two neutrons), emitted as a consequence of radioactivity;

It can be written as α-particle.

b brown mice / white sand dunes

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands