Assertion (A): Acetic acid, with a pKa value of 4.76, is considered t…

The correct answer is Option (3) → (A) is true but (R) is false.

The strength of an acid is shown by its pK_a value (pK_a = –log K_a): the smaller the pK_a, the stronger the acid. Acids are put into four classes by their pK_a values:

• Strong acids — pK_a less than 1

• Moderately strong acids — pK_a between 1 and 5

• Weak acids — pK_a between 5 and 15

• Extremely weak acids — pK_a more than 15

Assertion (A): Acetic acid, with a pK_a value of 4.76, is considered to be a moderately strong acid. — True. 4.76 lies between 1 and 5, so acetic acid falls in the class of moderately strong acids.

Reason (R): Acids with pK_a values between 5 and 15 are considered to be moderately strong acids. — False. Acids with pK_a values between 5 and 15 are weak acids; the moderately strong acids have pK_a values between 1 and 5.

NCERT (2026-27 edition):
8.9.1 Reactions Involving Cleavage of O–H Bond – “…The pK_a of hydrochloric acid is –7.0, where as pK_a of trifluoroacetic acid (the strongest carboxylic acid), benzoic acid and acetic acid are 0.23, 4.19 and 4.76, respectively.”

“Smaller the pK_a, the stronger the acid ( the better it is as a proton donor). Strong acids have pK_a values < 1, the acids with pK_a values between 1 and 5 are considered to be moderately strong acids, weak acids have pK_a values between 5 and 15, and extremely weak acids have pK_a values >15.”