A litre of buffer solution contains \(0.1\) mole of each of \( \mathrm{NH_3} \) and \( \mathrm{NH_4Cl} \). On the addition of \(0.02\) mole of \( \mathrm{HCl} \) by dissolving gaseous \( \mathrm{HCl} \), the pH of the solution is found to be _______ \( \times 10^{-3} \) (Nearest integer) [Given: \( pK_b(\mathrm{NH_3}) = 4.745 \), \( \log 2 = 0.301 \), \( \log 3 = 0.477 \), \( T = 298 \ \mathrm{K} \)]
