Question

what is the mass of 0.2 mole of oxygen atoms

Answer 1

Mass = no. of moles × atomic mass
=0.2 × 16
3.2
the mass = 3.2 g

Answer 2

0.2 moles of oxygen atom means
0.2/2 mole of oxygen molecules
I.e, 0.1 moles of oxygen atoms.
Molecular mass of 1 mole of oxygen molecule is 32g.
Therefore,
Mass of 0.1 mole of oxygen molecules is 0.1*32

=3.2gm
Hope u will understand.