Question

Which of the following substances is insoluble in water?

• A. HCl
• B. NaCl
• C. ${\text{N}}_2$
• D. KCl

Answer 1

The correct option is C ${\text{N}}_2$

We know that 'like dissolves like'. This means that polar solvents such as water readily dissolve polar covalent and ionic compounds in them.
From the given options, NaCl and KCl are ionic compounds, and HCl is a polar covalent compound, which means that all three of them readily dissolve in water. ${\text{N}}_2$ is a non-polar covalent compound and is hence insoluble in polar solvent like water.