Question

What is the Mass of 6.10^23 atoms of oxygen

Answer 1

We need to find amount of substance $n=\frac{N}{N_A}$ and then multiply it by oxygen molar mass

$m = \frac{N}{N_A}M = \frac{6\times10^{23}}{6.02\times10^{23}mol^{-1}}\times32\frac{g}{mol} \approx 31.89g$

(What Avogadro constant value do you use? If it's 6*10^23 the answer would be 32g)

Answer: 31.89g