Solubility of compounds in water
It is not. $\ce{NaOH}$ is more soluble ($&gt;100~\mathrm{g}/100~\mathrm{ml}$) then $\ce{NaCl}$ ($&lt;30 ~\mathrm{g}/100~\mathrm{ml}$). $\ce{NaOH}$ when dissolved produces $\ce{OH^-}$ anion, that has relatively small size and forms specific hydrogen bonds (where it is bonded to relatively small positively charged hydrogen) very well. In solid $\ce{NaOH}$ it has to form hydrogen bonds with quite big $\ce{Na^+}$ cation.