Question

how many oxygen atoms are present in 40 grams of O2 gas

Answer 1

hi friend
here's your answer looking for

as we know that 1 mole of any element will contain the same amount of number of atom or molecule.

so,

molecular mass of O2 = 16×2=32

so,

1mole of O2 weigh 32grams and contains
$6.022 \times {10}^{23}$
particles

hence,

40 grams of O2 will contain

$\frac{40}{32} \times 6.022 \times {10}^{23}$

$1.25(6.022 \times {10}^{23} ) \\ \\ = 9.033 \times {10}^{23} moecule$
but,

number of oxygen atom =

$2(9.033 \times {10}^{23} ) \\ \\ = 18.066 \times {10}^{23} or \: 1.8066 \times {10}^{24} atom$

so, this is your answer looking

hope you are satisfied with my answer

Answer 2

The answer is attached