Question

The number of atoms present in one mole of an element is equal to Avogadro's number. Which of the following element contains the greatest number of atoms?

(a) 4 g He

(b) 46 g Na

(c) 0.40 g Ca

(d) 12 g He

Answer 1

(d)

For comparing number of atoms, first we calculate the moles as all are monoatomic and hence, moles×NA = number of atoms.

Moles of 4 g He =44=1 mol

46 g Na=4623=2 mol

0.40 g Ca=0.4040=0.1 Mol

12 g He=124=3 mol

Hence, 12 g He contains greatest number of atoms as it possesses maximum number of moles.