If $(\pm)$ $2$-methylbutanoic acid is esterified by reaction with $(\pm)$ $2$-butanol,how many optically active compounds will be present in the final equilibrium reaction mixture?

What is the correct order of acidic strength for the following compounds: $(a)$ Phenol,$(b)$ $p$-methylphenol,$(c)$ $p$-methylbenzoic acid,and $(d)$ Benzoic acid?

Arrange the following compounds in increasing order of their property as indicated:
$(i)$ Acetaldehyde,Acetone,Di-tert-butyl ketone,Methyl tert-butyl ketone (reactivity towards $HCN$)
$(ii)$ $CH_3CH_2CH(Br)COOH$,$CH_3CH(Br)CH_2COOH$,$(CH_3)_2CHCOOH$,$CH_3CH_2CH_2COOH$ (acid strength)
$(iii)$ Benzoic acid,$4$-Nitrobenzoic acid,$3,4$-Dinitrobenzoic acid,$4$-Methoxybenzoic acid (acid strength)

Product $(A)$ of the reaction is:

Match Column-$I$ with Column-$II$ :
| Column-$I$ | Column-$II$ |
| :--- | :--- |
| $(A)$ Cyclopentanone + $2,4-$$DNP$ $\xrightarrow{\text{mild } H^+}$ Cyclopentanone$-2,4-$$DNP$ derivative | $(P)$ Electrophilic substitution |
| $(B)$ $4-$phenyl$-2-$methylbutan$-2-$ol $\xrightarrow{\text{Conc. } H_2SO_4}$ $1,1-$dimethyl$-1,2,3,4-$tetrahydronaphthalene | $(Q)$ Nucleophilic substitution |
| $(C)$ $4-$chlorocyclohexanethiol $\xrightarrow{\text{Base}}$ $7-$thiabicyclo[$2.2$.$1$]heptane | $(R)$ Nucleophilic addition |

Which of the following compounds will undergo decarboxylation on heating?