Which of the following requires a critical mass?
a) fission
b) gamma emission
c) beta emission
d) lepton

A) fission

Explanation:

Fission reactions require a critical mass. The critical mass is necessary because it makes a fission reaction self sustaining. This critical mass is the minimum amount of material required. Nuclear fission additionally depends on the composition, purity and concentration of the fissile material. Critical mass is important in the design of nuclear warheads.

the answer is 1260

you spend 7 hours in school for 1 school day with 5 school days in 1 school week with 36 school weeks in a school year.

7*5*36= 1260 it's all about multiplying