$(i) \ F_3CCOOH$
$(ii) \ CH_3COOH$
$(iii) \ C_6H_5COOH$
$(iv) \ CH_3CH_2COOH$
Correct order of $pK_a$ value is:

In the following sequence of reactions,a compound $A$ (molecular formula $C_{6}H_{12}O_{2}$) with a straight chain structure gives a $C_{4}$ carboxylic acid. $A$ is :
$A$ $\xrightarrow{LiAlH_{4} / H_{3}O^{+}} B$ $\xrightarrow{\text{Oxidation}} C_{4} \text{ carboxylic acid}$

The product of the reaction is:

Provide identification tests for the following pairs of compounds:
$(1)$ Phenol and carboxylic acid
$(2)$ Formic acid and acetic acid
$(3)$ Acetic acid and ethanol
$(4)$ Acetic acid and acetone
$(5)$ Aldehyde and ketone
$(6)$ Acetaldehyde and acetone
$(7)$ Acetaldehyde and formaldehyde
$(8)$ Benzaldehyde and acetaldehyde

When compound $X$ is oxidised by acidified potassium dichromate,compound $Y$ is formed. Compound $Y$ on reduction with $LiAlH_4$ gives $X$. $X$ and $Y$ respectively are:

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 |