What is the term that is used to describe a key factor required to start a fission reaction?
chain reaction
critical mass
neutron absorption
neutron moderation

The correct option is neutron absorption

Nuclear fission is the reaction in which a big nucleus is divided into smaller nuclei. The reaction is very dangerous and it is handled very carefully. It can be started by bombarding slow neutrons on a bigger nucleus. Since bombarding is actually inducing the neutron so we can refer it to absorption too. Therefore, the correct answer is absorption

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.