Identifying base in a chemical equation
I would write down the half equations for each reaction:
A

$\ce{ HNO3 + H+ -&gt; H2NO3+ }$ (Base)
$\ce{H2SO4 -&gt; HSO4- + H+}$  (Acid)

B

$\ce{  HSiO3- -&gt; SiO2 + OH- }$  (Base)
$\ce{HCN  -&gt; CN- + H+ }$ (Acid)

C

$\ce{HNO2 -&gt; NO2- + H+ }$ (Acid)
$\ce{HCO3- -&gt; CO2 + OH- }$(Base)

D

$\ce{C6H5O- + H+ -&gt; C6H5OH }$ (Base)
$\ce{CH2ClCO2H -&gt; CH2ClCO2- + H+ }$(Acid)