Q128
General ScienceChemistry
If 14 gm of $\mathrm{N_2}$ has '$n$' number of molecules, how many molecules are present in 46 gm $\mathrm{NO_2}$?
- a.$n$
- b.$2n$
- c.$\frac{n}{2}$
- d.$\frac{3n}{2}$
Answer: (B) $2n$
Equal numbers of moles contain equal numbers of molecules. 14 g of $\mathrm{N_2}$ (molar mass 28) is $\frac{14}{28} = 0.5$ mole and contains $n$ molecules, so 1 mole contains $2n$ molecules. 46 g of $\mathrm{NO_2}$ (molar mass $14 + 32 = 46$) is exactly 1 mole and therefore contains $2n$ molecules. Option A assumes equal masses mean equal molecules, the usual mistake. One mole of any substance contains Avogadro's number of particles, $6.022 \times 10^{23}$, and one mole of any gas occupies 22.4 litres at STP.