10 mL of 0.1 M-HCI solution is added in 90 mL of a buffer solution having 0.1 `M-NH_(4)OH` and 0.1 `M-NH_(4)CI`. The percentage change in pH of solution is `(K_(a) " of " NH_(4)^(+) = 5xx10^(-10))`[log 2 = 0.3] :
A. `(10)/(4.7) %` increase
B. `(10)/(4.7) %` decrease
C. `(10)/(9.3) %` increase
D. `(10)/(9.3) %` decrease
