Question

Which one of the following contains same number of atoms as there are in $12$ grams of magnesium?

• A. $12$ grams carbon
• B. $40$ grams of calcium
• C. $16$ grams of oxygen
• D. $7$ grams of carbon monoxide

Answer 1

The correct option is D $7$ grams of carbon monoxide

$No.ofatoms$ $=\frac{Weight}{MolecularWeight}\times N_A\times atomicity$

$N_A$ is the Avogadro number.

$12$ g of magnesium corresponds to $\frac{12}{24}=0.5$ moles of magnesium. It contains $0.5N_A$ magnesium atoms.

$12$ g of carbon corresponds to $\frac{12}{12}=1$ mole of carbon. It contains $N_A$ carbon atoms.

$40$ g of calcium corresponds to $\frac{40}{40}=1$ mole of calcium. It contains $N_A$ calcium atoms.

$16$ g of oxygen corresponds to $\frac{16}{32}=0.5$ moles of $O_2$. It contains $0.5N_A\times 2=N_A$ atoms of $O_2$.

$7$ g of CO corresponds to $\frac{7}{28}=0.25$ mole of CO. It contains $0.25\times 2=0.5N_A$ atoms of CO.

Hence, option D is correct.