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

Options

A. 4 g He
B. 46 g Na
C. 0.4 g Ca
D. 12 g He

Explanation

(a) 1 mol of He = 4g = `N_A` atoms
or 4 g of He `4/4mol=1N_A` atom
(b) 1 mole of Na = 23g = `N_A` atoms
[ `therefore " no. of moles" = ("given mass")/("atomic mass")`
`therefore " 46g of Na " = 46/23 " mol " = 46/23 N_A " atoms " = 2N_A` atoms
(c) 1 moles of Ca = 40 g =`N_A` atoms
`therefore " 0.40g of Ca " =(0.40)/(40) " mol " =(0.40)/(40) N_A` atoms
`=0.01 N_A` atoms
(d) 1 mole of He = 4g `=N_A` atoms
`therefore " 12g of He " =12/4 " mol " =12/4 N_A " atoms " = 3N_A` atoms