Both (A) and (R) are true statement but (R) is not the correct explanation of (A). pH of a buffer solution is given by Henderson-Haselbalch equation. ‌pH‌=pKa+log‌
[‌ salt ‌]
[‌ acid ‌]
∴‌pH‌=pKa(‌ when ‌[‌ salt ‌]=[‌ acid ‌])