${10^{ - 12}} = {10^{ - 2}} \times {\alpha ^2}$; ${\alpha ^2} = {10^{ - 10}}$; $\alpha = {10^{ - 5}}$
$[O{H^ - }] = C\alpha = .01 \times {10^{ - 5}} = {10^{ - 7}}$
$A = NH_4Cl$; $ B = CH_3COONa$; $ C = NH_4OH$; $D = CH_3COOH$