The catalyst used in the contact process is

Male gametes are flagellated in

At room temperature,a $P-$ type semiconductor has

The structure of $IF_7$ is $......$ .

When a body of mass $1.0\, kg$ is suspended from a certain light spring hanging vertically,its length increases by $5\, cm$. By suspending a $2.0\, kg$ block to the spring,if the block is pulled through $10\, cm$ and released,the maximum velocity in $m/s$ is: (Acceleration due to gravity $g = 10\, m/s^2$)

If the bond energies of $H-H$,$Br-Br$ and $H-Br$ are $433$,$192$ and $364 \ kJ \ mol^{-1}$ respectively,$\Delta H^o$ for the reaction $H_{2(g)} + Br_{2(g)} \to 2HBr_{(g)}$ is.....$kJ$