Which of the following homologous series has an incorrect general formula?

Arrange benzene,$n$-hexane and ethyne in decreasing order of their acidic behaviour.

Provide a chemical test to distinguish between butane and but-$1$-ene and write the corresponding reactions.

Match the following reactions in List-$I$ with their products in List-$II$:
| List-$I$ | List-$II$ |
| :--- | :--- |
| $A. HC \equiv CH \xrightarrow{Hg^{2+}, H^{+}/H_{2}O}$ | $I. H_{3}C-COOH$ |
| $B. CH_{4} \xrightarrow{O_{2}, Mo_{2}O_{3}, \Delta}$ | $II. CH_{3}-CO-CH_{3}$ |
| $C. (CH_{3})_{2}C=C(CH_{3})_{2} \xrightarrow{O_{3}, Zn, H_{2}O}$ | $III. H_{3}C-CHO$ |
| $D. CH_{3}-CH=CH-CH_{3} \xrightarrow{KMnO_{4}, H^{+}}$ | $IV. HCHO$ |

The order of reactivity of $C_2H_6$,$C_2H_4$,and $C_2H_2$ is.......

The correct order of heat of hydrogenation of the given molecules is: