Question

An atom of potassium-37 and an atom of potassium-42 differ in their total number of

Answer 1

³⁷K and ⁴²K

Both atoms are of the same element. which means they have the same atomic number. Atomic number is the number of protons. Atomic number is characteristic for the element. Both having the same atomic number means they both have the same number of protons

the superscripts are for their masses. Atomic mass is the sum of the protons and neutrons. the 2 K atoms have different masses but same number of protons

which means the number of neutrons vary. These are called isotopes. Isotopes are atoms of the same element with different numbers of neutrons.

therefore An atom of potassium-37 and an atom of potassium-42 differ in their total number of neutrons

Answer 2

K-37 and K-42 are isotopes of eachother
Isotopes have the same number of protons (And therefore electrons), but different numbers of neutrons
So the answer is (2)