Question

In an atom of argon-40, the number of protons
(1) equals the number of electrons
(2) equals the number of neutrons
(3) is less than the number of electrons
(4) is greater than the number of electrons

Answer 1

(1) equals then number of electrons is your answer. If it is not a charged ion (and an ion of argon is rare naturally) than the number of protons always equals the number of electrons.

Answer 2

(1) equals the number of electrons

Because in argon-40, its protons and electrons are both 18, while the neutrons are different.