Question

what is the atomic number of an atom?
the row of the periodic table to which it belongs
the number of protons it contains
the number of naturally occurring isotopes it has
the number of neutrons it contains

Explanation:

The atomic number of an atom is defined as the number of protons in its nucleus. The row in the periodic table is related to electron - shell energy levels, the number of isotopes is about different forms of the same element with different neutron numbers, and the number of neutrons is different from the atomic number.

Answer:

The number of protons it contains