Question

How many moles of helium will have a mass equal to the mass of 1 mole of oxygen gas?

• A. 8
• B. 4
• C. 16
• D. 2

Answer 1

The correct option is A 8

$\bullet$ Helium exists as a monoatomic gas (He) whereas oxygen gas is a diatomic molecule ($O_2$).

$\bullet$ Gram molecular mass of a substance is the sum of gram atomic masses of the constituent atoms.

Gram molecular mass of $O_2$ = $2\times 16$ g = 32 g.

Gram atomic mass of He = 4 g

Let us assume that the mass of $x$ moles of helium is equal to the mass of one mole of oxygen gas.
$4x=32⟹x=8$

So, 8 moles of helium gas will have a mass equal to that of 1 mole of oxygen gas.