The atomic mass of silicon is approximately 28.055. which of the following would indicate the number closest to 28.055?
1. atomic number
2. mass number
3. number of electrons + neutrons
4. number of protons + electrons

2. mass number

Explanation:

Mass number is equal to the sum of protons + neutrons in an element. For silicon is 14 + 14 = 28 (for the silicon 14 isotope).

2. mass number

Explanation:

The atomic mass is concentrated in the tiny nucleus which contains protons and neutrons. These particles are called the nucleons. Nucleons dictate the mass of an atom.

The number of protons and neutrons in a nucleus is the atomic mass. Also, when we add the protons and neutrons together, we are calculating the mass number. The mass number also gives the atomic mass.

Atomic number on the other hand is the number of electrons or protons in a neutral atom.