For the following reaction sequence, choose the correct option

The first step is the Friedel-Crafts acylation of benzene with acetyl chloride ($\text{CH}_3\text{COCl}$) and anhydrous $\text{AlCl}_3$, which produces acetophenone ($\text{C}_6\text{H}_5\text{COCH}_3$).

The second step is the haloform reaction. Acetophenone has a methyl ketone group and reacts with sodium hypochlorite ($\text{NaOCl}$) to form sodium benzoate ($\text{C}_6\text{H}_5\text{COONa}$) and chloroform ($\text{CHCl}_3$).

Thus, the products $\text{P}$ and $\text{Q}$ are sodium benzoate and chloroform.

Sodium benzoate ($\text{P}$) on acidification yields benzoic acid ($\text{C}_6\text{H}_5\text{COOH}$).

Chloroform ($\text{Q}$) on exposure to air and light oxidizes to form phosgene ($\text{COCl}_2$), a highly poisonous gas, according to the reaction:
$2\text{CHCl}_3 + \text{O}_2 \xrightarrow{\text{light}} 2\text{COCl}_2 + 2\text{HCl}$

Therefore, if $\text{P}$ gives a carboxylic acid on acidification, $\text{Q}$ gives a poisonous gas on exposure to air and light.

Answer: If $\text{P}$ gives a carboxylic acid on acidification, $\text{Q}$ gives a poisonous gas on exposure to air and light.