Question

1. the mass number of an isotope is equal to: *

a) protons only
b) neutrons only
c) protons + neutrons
d) protons + electrons

1. hydrogen - 1, hydrogen - 2, and hydrogen - 3 are examples of: *

a) elements
b) molecules
c) isotopes
d) compounds

Explanation:

For question 3, the mass number of an isotope is the sum of protons and neutrons in the nucleus of an atom. Electrons have negligible mass compared to protons and neutrons and are not included in mass - number calculation. For question 4, Hydrogen - 1, Hydrogen - 2, and Hydrogen - 3 are isotopes of hydrogen as they have the same number of protons but different numbers of neutrons.

Answer:

1. c) Protons + Neutrons
2. c) Isotopes