An atom with an atomic number of 12 and a mass number of 25 can best be described by which of these? a) an atom that contains 12 protons and 13 neutrons. b) an atom that contains 13 protons and 12 neutrons. c) an atom that contains 12 protons and 25 neutrons. d) an atom that contains 25 protons and 12 neutrons.

A) An atom that contains 12 protons and 13 neutrons.

Explanation:

An element consists of three components that determines its charge and the mass number. These components are the proton number, electron number and neutron number. The mass number, denoted by A, is the sum of the proton number and the number of neutrons in the atom of that element.

The proton number determines the atomic number of an element (Z). An element that is neutrally charged will contain equal number of proton and electrons. A positively charged atom will contain more protons than electrons while a negatively charged atom will contain vice versa.

Hence, to get the number of neutrons in the atom, one will subtract the proton number from the mass number i.e. A - Z

Therefore, in this question of an atom that contains atomic number of 12 and a mass number of 25, the neutron number will be 25 - 12 = 13.

Thus, the proton number=atomic number is 12 and the neutron number is 13.