$pH$ of 0.01 M $(NH_4)_2SO_4$ and 0.02 M $NH_4OH$ buffer ($pK_a$ of $NH_4^+$ = 9.26) is

Question

(a) 4.74 + log 2

(b) 4.74 - log 2

(c) 9.26 + log 2

(d) 9.26 + log 1