How does critical mass play a role in nuclear reactions?

it is the minimum amount of material needed to start a fission reaction.
it is the minimum amount of material needed to start a fusion reaction.
it is the minimum amount of material needed to sustain a fission reaction.
it is the minimum amount of material needed to sustain a fusion reaction.

The correct answer for above statement is:

c.It is the minimum amount of material needed to sustain a fission reaction.

Explanation:

A nuclear reaction is taken into account to be the method during which 2 nuclear paticles (two nuclei or a nucleus and a nucleon) move to supply 2 or a lot of nuclear particles or gamma rays.

Thus, a natural action should cause a change of a minimum of one nuclide to a different. typically if a nucleus interacts with another nucleus or particle while not dynamic the mature of any nuclide, the method is mentioned a nuclear scattering.

The important mass is that the smallest amount of fissile material required to sustain nuclear reactions below expressed conditions

the total distance traveled by the car is

30km + 49km = 79 km .