Beryllium hydride is made from $\mathrm{BeCl}{}_2$ and $\mathrm{LiAlH}{}_4$. It is hydrolysed completely by water to give a gas and a hydroxide, and that hydroxide dissolves in excess aqueous $\mathrm{NaOH}$. Which option gives the number of hydrogen neighbours of each Be in solid $\mathrm{BeH}{}_2$ and the beryllium species in the final solution?

1. A4; $[\mathrm{Be}(\mathrm{OH}){}_4]{}^{2-}$
2. B4; $[\mathrm{Be}(\mathrm{OH}){}_3]{}^{-}$ with no other beryllium species
3. C2; $\mathrm{Be}{}^{2+}$
4. D2; $[\mathrm{Be}(\mathrm{OH}){}_4]{}^{2-}$