Question

calculate the number of atoms in . (a) 52 moles of He. (b) 52 g of He. (c) 52 u of He

Answer 1

Atomic mass of Helium is 4u = 2protons + 2 Neutrons = 1 atom 
No. of atoms in 52u = 52/4 = 13 atoms

52g of heliume
6.022*10^23*52/4 atoms of he
7.829*10^24 atoms of he

1mole of he =6.023*1023