The atomic mass of an element can be approximated by adding the number of plus the average number of
a. protons; electrons
b. protons; neutrons
c. neutrons; electrons

Option (B) is the correct answer.

Explanation:

Atomic mass is defined as the summation of total number of protons and neutrons present in an element.

On the other hand, atomic number means the total number of protons present in an element.

For example, atomic number of sodium is 11 and number of neutrons present in it are 12.

Hence, atomic mass of sodium = no. of protons + no. of neutrons

                                                    = (11 + 12) amu

                                                    = 23 amu

Therefore, we can conclude that the atomic mass of an element can be approximated by adding the number of protons plus the average number of neutrons.

1.solid

2.carbon dioxide

3.helium

it is b that is the answer.