What is the atomic mass of
an atom?

1 unit

Explanation:

It is expressed as a multiple of one-twelfth the mass of the carbon-12 atom, 1.992646547 × 10−23 gram, which is assigned an atomic mass of 12 units.

1/12 * 12 = 1. I think so.

answer; ///i do believe that the correct answer is (b); ///particle composed of two or more atoms bonded together;