તો ${\text{pH}} = {\text{7}}\,\, + \frac{{\text{1}}}{{\text{2}}}pKa - \frac{1}{2}pKb$
$pH = 7 + \frac{1}{2} \times 4 - \frac{1}{2} \times 5$
$pH = 7 + 2 - 2.5 = 6.5$