Answer : The correct option is Acid.
Explanation :
- Acid : Acids are those which accepts an electron-pairs.
- Base : Bases are those which donates ab electron-pairs.
- Alkali : It is a base that dissolves in water. It is basically a base and the pH greater than 7.
- Hydroxide ion : It is a poly-atomic ion which is negatively charged.
Therefore, the acid is a substance which accepts an electron-pair.