Which of the following gases contains the least number of atoms at s.t.p?

A.

1 mole of butane

B.

4 moles of chlorine

C.

3 moles of ozone

D.

7 moles of argon

Correct answer is D

4 moles of chlorine gas = 4Cl\(_2\) = 8 atoms of chlorine
3 moles of ozone = 3O\(_3\) = 9 atoms of oxygen
1 mole of butane = C\(_4\)H\(_{10}\)
7 mole of argon = 7Ar = 7 atoms of argon

Argon is a monoatomic noble gas with the least number of atoms.