This conversion can be achieved by

Formaldehyde can be distinguished from acetaldehyde by the use of

Which of the following aldehydes gives a red precipitate with Fehling solution?

Match the reactions in Column-$I$ with their products in Column-$II$.
| Column-$I$ (Reagents) | Column-$II$ (Product) |
| :--- | :--- |
| $(A) \ CH_3CHO + 2C_2H_5OH \xrightarrow{HCl_{(g)}} $ | $(i) \ (CH_3)_2C(OCH_2)_2$ |
| $(B) \ CH_3COCH_3 + CH_2OH-CH_2OH \xrightarrow{HCl_{(g)}} $ | $(ii) \ CH_3CH(OH)CN$ |
| $(C) \ CH_3CHO + HCN$ $\xrightarrow{OH^-}$ $\xrightarrow{H_3O^+}$ | $(iii) \ CH_3CH(OC_2H_5)_2$ |
| $(D) \ CH_3CHO + HCN \xrightarrow{OH^-} $ | $(iv) \ CH_3CH(OH)COOH$ |

$3-\text{Hydroxybutanal}$ is formed when $X$ reacts with $Y$ in dilute $Z$ solution. What are $X, Y$ and $Z$? $(X, Y, Z)$

Hex$-4-$en$-2-$ol on treatment with $PCC$ gives $'A'.$ $'A'$ on reaction with sodium hypoiodite gives $'B',$ which on further heating with soda lime gives $'C'.$ The compound $'C'$ is $....... .$