Answer: Option (a) is the correct answer.
Explanation:
A base is a substance that gives hydroxide ions ([tex]OH^{-}[/tex]) upon dissociation in water. This means that a base increases the hydroxide ion concentration in a solution.
On the other hand, an acid is a substance that gives hydrogen ions ([tex]H^{+}[/tex]) upon dissociation in water. This means that an acid increases the hydrogen ion concentration in a solution.
For example, [tex]S^{2-} + H_{2}O \rightarrow OH^{-} + SH^{-}[/tex]
Since, sodium sulfide ([tex]Na_{2}S[/tex]) dissociates to give hydroxide ions.
Hence, we can conclude that [tex]Na_{2}S[/tex] is a base because it ionizes to release [tex]OH^{-}[/tex].
