Which one of the following pairs will form an ideal solution?

The correct answer is Option (3) → $n$-hexane and $n$-heptane ##

$n$-hexane and $n$-heptane will form an ideal solution over entire range of concentrations as their intermolecular interactions (solute-solvent) after forming solution are similar to their intermolecular attractions (solute-solute, solvent-solvent) before mixing the components.