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.

conduction is the transfer of thermal energy (heat in transfer) due to collisions between the molecules in the object. collisions between adjacent atoms and molecules transfer kinetic energy from the warmer to the cooler object. the objects must be in physical contact.