The relationship between pressure and moles, when volume and temperature of a gas are held constant, is: P/n = k. We could say then, that:?

P/n = k
Hence, P₁/n₁ = P₂/n₂, and thus n₁/n₂ = P₁/P₂

A) is false. If the number of moles is doubled, the pressure is doubled, but not halved.
B) is false. If the number of moles is halved, the pressure is halved, but not doubled.
C) is true.
D) is false. If the number of moles is halved, the pressure is halved, but not quadrupled.

The answer: C) If the number of moles is tripled, the pressure also triples.

P/n = k
P = nk
pressure and number of moles are proportional
C) If the number of moles is tripled, the pressure also triples.

P * V = n * R * T

Let the gas be at standard temperature. R = 22.4 ÷ 273

1 * V = n * (22.4 ÷ 273) * 273
V = n * 22.4
V ÷ n = 22.4

This means the volume and the number of moles are directly proportional to each other. So C is the only correct answer. I hope this is helpful for you.