Which of the following statements about the bisulphite addition product of an aldehyde are correct?

1. AIt is freely soluble in diethyl ether.
2. BIt is the sodium salt of an alpha-hydroxy sulphonic acid, formed by attack of sulphur of $\mathrm{HSO}{}_3{}^{-}$ on the carbonyl carbon.
3. CIt can be used to separate an aldehyde from a non-carbonyl organic impurity by extraction.
4. DIt can be decomposed to the aldehyde with dilute acid or with aqueous sodium carbonate.