$k=\frac{2.303}{t} \log \frac{100}{100-99}$
$\frac{0.693}{6.93}=\frac{2.303}{t} \log \frac{100}{1}$
$\frac{0.693}{6.93}=\frac{2.303 \times 2}{t}$
$\Rightarrow t=46.06\, \mathrm{min}$
$N{H_2}N{O_{2\left( {aq} \right)}} + OH_{\left( {aq} \right)}^ - \to NHNO_{2\left( {aq} \right)}^ - + {H_2}{O_{\left( l \right)}}$
$NHNO_{2\left( {aq} \right)}^ - \to {N_2}{O_{\left( {aq} \right)}} + OH_{\left( {aq} \right)}^ - $