JEE Main · 2023 · 10 Apr 2023 · Shift 2 · Chemical Bonding and Molecular Structure

Count the lone pairs on each molecule. Water has two lone pairs on oxygen. In ${\mathrm{N}}_2$, written $:\mathrm{N}\equiv \mathrm{N}:$, each nitrogen carries one lone pair, giving two in all. In CO, written $:\mathrm{C}\equiv \mathrm{O}:$, carbon and oxygen each carry one lone pair, giving two. Nitric oxide, written with an $\mathrm{N}\equiv \mathrm{O}$ framework and its odd electron, likewise carries one lone pair on each atom, so it has two. Ammonia has one lone pair, $\mathrm{Xe}{\mathrm{F}}_4$ has far more than two, carbon dioxide has four and ${\mathrm{F}}_2$ has six. The number of molecules with exactly two lone pairs is 4.