Question

Among the following acids which has the lowest $p{k}_a$ value?

• A. $C{H}_{3}C{H}_{2}COOH$
• B. $(C{H}_3{)}_{2}CHCOOH$
• C. $HCOOH$
• D. $C{H}_{3}COOH$

Answer 1

The correct option is C $HCOOH$

Lowest $p{k}_a\to$ Highest $k_a\to$ High acididty.

As $R$ increases, acidity decreases in carboxylic acid due to increase in electron density on $O-H$ bond.

Where, $R$ is length of alkyl chain.

So, $HCOOH$ is more acidic and least value of $p{k}_a$

Hence, option $C$ is correct.