Number of Atoms & Number of Molecules

Which of the following substance contains 1.204 x 10²⁴ atoms?

A  1 mol of nitrogen gas
B  1 mol of ammonia
C  1 mol of water
D  1 mol of argon

Many of my students choose the wrong answer in the current topical test.

1 mol of nitrogen gas consists of 1 x 6.02 x 10²³ molecules. 

Number of atoms in 1 mol of nitrogen gas is 2 x 6.02 x 10²³ .
(Each nitrogen, N₂ molecule consists of 2 nitrogen atoms)

1 mol of ammonia consists of 1 x 6.02 x 10²³ molecules

Number of atoms in 1 mol of ammonia gas is 4 x 6.02 x 10^23.
(Each ammonia, NH₃ molecule consists of 4  atoms) 

1 mol of water consists of 1 x 6.02 x 10²³ molecules

Number of atoms in 1 mol of water is 3 x 6.02 x 10²³
(Each water, H2O molecule consists of 3 atoms) 

1 mol of argon consistss of 1 x 6.02 x 10²³ atoms. 


The correct answer : A