Which of the following reagents is used to obtain acetic anhydride from acetyl chloride?

Which of the following compounds is used as a food preservative?

Which of the following compounds reacts with $NaHCO_3$ solution to produce a sodium salt and $CO_2$ gas: phenol,acetic acid,or $n$-hexanol?

Assertion : $\beta$-Keto carboxylic acids lose $CO_2$ when heated at about $370 \ K$.
Reason : An enol is first formed by loss of $CO_2$,but it readily tautomerises to the more stable ketone.

Correct order of $pK_{a}$ of given compounds is $:-$
$(P) \ CH_{3}COOH$
$(Q) \ FCH_{2}COOH$
$(R) \ ClCH_{2}COOH$
$(S) \ C_{2}H_{5}COOH$

The reaction of $HCOOH$ with conc. $H_2SO_4$ gives