Which one of the following statements is NOT correct?

At STP, $1$ mole of any ideal gas occupies $22.4$ litres.

Half mole of nitrogen gas occupies $\dfrac{1}{2} \times 22.4 = 11.2$ litres. This statement is correct.

Molar mass of ammonia ($NH_3$) is $17$ g/mol. $17$ g of ammonia corresponds to $1$ mole, which contains $6.022 \times 10^{23}$ molecules. This statement is correct.

$22.4$ litres of $CO_2$ gas at STP corresponds to $1$ mole. The molar mass of $CO_2$ is $44$ g/mol, so it weighs $44$ grams. This statement is correct.

Molar mass of hydrogen gas ($H_2$) is $2$ g/mol. $4$ grams of hydrogen gas corresponds to $\dfrac{4}{2} = 2$ moles. The number of molecules in $2$ moles is $2 \times 6.022 \times 10^{23} = 1.2044 \times 10^{24}$ molecules. This statement is incorrect.

Answer: 4 gram of hydrogen gas contains $6.022 \times 10^{23}$ molecules