d
\(\begin{array}{l}
Max.\,height = H = \frac{{{v^2}{{\sin }^2}\left( {90 - \theta } \right)}}{{2g}}\,\,\,....\left( i \right)\\
Time\,of\,flight,\,T = \frac{{2\,v\,\sin \left( {90 - \theta } \right)}}{g}\,\,\,\,\,...\left( {ii} \right)\\
From\left( i \right),\,\frac{{v\,\cos \,\theta }}{g} = \sqrt {\frac{{2H}}{g}} \,From\,\left( {ii} \right),\\
T = 2\sqrt {\frac{{2H}}{g}}  = \sqrt {\frac{{8H}}{g}} .
\end{array}\)