Let me explain every term given in the options.
critical mass - the minimum amount of a given fissile material necessary to achieve a self-sustaining fission chain reaction under stated conditions.
doping- In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties.
bombardment-nuclear reaction, change in the identity or characteristics of an atomic nucleus, induced by bombarding it with an energetic particle. The bombarding particle may be an alpha particle, a gamma-ray photon, a neutron, a proton, or a heavy ion.
saturation- Saturation means holding as much moisture as possible.
