In which of the following are Chlorophyll-$a$,Chlorophyll-$d$,and Phycoerythrin found?

Given that $\Delta H_f(H) = 218 \ kJ/mol$,express the $H-H$ bond energy in $kcal/mol$.

$A$ particle of mass $4 m$ explodes into three pieces of masses $m, m$ and $2 m$. The equal masses move along $X$-axis and $Y$-axis with velocities $4 ms^{-1}$ and $6 ms^{-1}$ respectively. The magnitude of the velocity of the heavier mass is

$\sec h^{-1}\left(\frac{1}{2}\right)-\operatorname{cosec} h^{-1}\left(\frac{3}{4}\right)$ is equal to

One energy difference between the states $n = 2$ and $n = 3$ is $E \, eV$ in a hydrogen atom. The ionization potential of the $H$ atom is ........... $E$.

The catalyst used for the polymerization of olefins is....