1. We identify compound $A$ first.

   The question says a toxic compound $A$ reacts with $\text{NaCN}$ in aqueous acidic medium to give an edible cooking component and food preservative $B$.

   A very common edible cooking component and preservative is acetic acid (vinegar).

2. Check how acetic acid can be formed from a toxic compound using $\text{NaCN}/\text{H}^+$.

   Methanol can first be converted to a cyanide derivative and then hydrolyzed to acetic acid overall. In practical organic chemistry, this corresponds to chain extension via cyanide followed by hydrolysis.

   So: $A = \text{methanol}, \qquad B = \text{acetic acid}$

3. Now convert $B$ to $C$ using diborane.

   Diborane can reduce carboxylic acids to primary alcohols: $\text{CH}_3\text{COOH} \xrightarrow{B_2H_6} \text{CH}_3\text{CH}_2\text{OH}$

   Hence, $C = \text{ethanol}$

   Ethanol is indeed used as a petrol additive (blended fuel) to reduce emissions.

4. Now convert $C$ to $D$ using oleum at $140^\circ C$.

   Ethanol on dehydration at about $140^\circ C$ in acidic medium gives diethyl ether: $2\,\text{C}_2\text{H}_5\text{OH} \xrightarrow[140^\circ C]{\text{conc. acid / oleum}} \text{C}_2\text{H}_5-O-\text{C}_2\text{H}_5 + H_2O$

   Diethyl ether is a well-known inhalation anesthetic.

   Therefore, $D = \text{diethyl ether}$

5. Match with options.

   The sequence is: $A = \text{Methanol}, \quad B = \text{acetic acid}, \quad C = \text{ethanol}, \quad D = \text{diethyl ether}$

   This matches Option A.

6. Verification of other options:

   • B: acetonitrile is not an edible cooking component/preservative.
   • C: formaldehyde is not edible and chloroform is not obtained this way.
   • D: 2-hydroxypropanoic acid is lactic acid, not the stated food preservative in this context.

Therefore, the correct answer is Option A.