Question

Some type of salts or acid/base are given In List-II and their pH calculation formula Is given In List-I by considering "a" much smaller than unity.

List-I (pH)	List-II
P. $\left[pK_w-\frac{1}{2}(pK_b-\log C)\right]$	1. Salt of a weak monobasic acid and a weak monoacidic base
Q. $\frac{1}{2}[pK_w+pK_a+\log C]$	2. Salt of weak monobasic acid and a strong base
R. $\frac{1}{2}[pK_w+pK_a-pK_b]$	3. Weak monoacidic base
S. $\frac{1}{2}[pK_w-pK_b-\log C]$	4. Salt of strong acid and a weak monoacidic base
	5. Weak monobasic acid

• A. 1-R, 2-Q, 3-P, 4-S
• B. 1-R, 3-P
• C. 1-R, 3-P, 2-Q
• D. 1-R, 3-P, 4-S

Answer 1

Answer: (B)

1-R, 3-P

Answer 2

The pH of a weak monoacidic base (concentration C, $K_b$) is $pH = \frac{1}{2}(2pK_w - pK_b + \log C)$, matching P. The pH of a salt of a weak monobasic acid and a weak monoacidic base is $pH = \frac{1}{2}(pK_w + pK_a - pK_b)$, matching R. Other formulas in List-I do not precisely match the standard derivations for the remaining species in List-II due to sign conventions or missing standard formulas.