Explanation

(c)
(i)Alkene and alkynes both react with $KMnO_{4}$ and decolourise it.
(ii)Only alkynes react with $AgNO_{3}$ to give white precipitate.
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$\therefore$ $C_{2}H_{4}$ (an alkene) reacts with $KMnO_{4}$ and decolourises it and does not react with $AgNO_{3},\ C_{2}H_{6}\ and\ CH_{4}$ are alkane they do not react with $KMnO_{4}\ and\ NaOH$.