Question

46 g of Na atoms (Number from mass)

Answer 1

1 mol of Na weights 23 gm

so 46 gm will have,
46/23 = 2 mol of Na atoms

so,number of atoms = 2 × 6.023×10²³
that is, 12.046 × 10²³ Na atoms

That's it
Hope it helped (≧▽≦)