Question

Which of the following would contain the same number of atoms as $12g$ of magnesium? (At. wt: $Mg=24;C=12;Ca=40$)

• A. $12g$ of carbon
• B. $20g$ of calcium
• C. $32g$ of oxygen
• D. $40g$ of potassium

Answer 1

Answer: (B)

$20g$ of calcium

• moles of C = $\frac{12}{12}=1$
• moles of Ca = $\frac{20}{40}=0.5$
• moles of O = $\frac{32}{16}=2$
• moles of K = $\frac{40}{39}=1.025$
  

As 1 mole of every element contains Avogadro number of atoms. Hence, Equal number of moles of different elements will contain same number of atoms. Therefore, 12 g of Magnesium will have same number of atoms as in 20 g of Calcium.