What is the number of protons in the nucleus of an atom equivalent to?

a. number of neutrons

b. atomic number

c. mass number

d. atomic weight

atomic number

Explanation:

the number of protons in the nucleus is called atomic number, it also equals the number of electrons

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.