What are control rods in a nuclear reactor?

$A$ $\gamma$-ray photon creates an electron-positron pair. If the rest mass energy of an electron is $0.51 \, MeV$ and the total kinetic energy of the electron-positron pair is $0.78 \, MeV$,then the energy of the $\gamma$-ray photon in $MeV$ is:

$A$ fission reaction is given by ${ }_{92}^{236} U \rightarrow{ }_{54}^{140} Xe +{ }_{38}^{94} Sr + x + y$,where $x$ and $y$ are two particles. Considering ${ }_{92}^{236} U$ to be at rest,the kinetic energies of the products are denoted by $K_{Xe}, K_{Sr}, K_x (2 \ MeV)$ and $K_y (2 \ MeV)$,respectively. Let the binding energies per nucleon of ${ }_{92}^{236} U, { }_{54}^{140} Xe$ and ${ }_{38}^{94} Sr$ be $7.5 \ MeV, 8.5 \ MeV$ and $8.5 \ MeV$ respectively. Considering different conservation laws,the correct option$(s)$ is(are):

The operation of a nuclear reactor is said to be critical when the value of the neutron multiplication factor $K$ is:

When $_3^7Li$ nuclei are bombarded by protons, and the resultant nuclei are $_4^8Be$, the emitted particles will be

Name of India's first nuclear reactor is