Atoms have positively charged particles, negatively charged particles, and particles with no charge. Why is an atom electrically neutral? O A Atoms have the same number of electrons (negative charge) and protons (positive charge).
o B. An atom's nucleus has only neutrons, which have no charge
OC. Atoms contain subatomic particles and not electrically charged particles
D. Atoms have neutrons and protons in the nucleus, and they do not have a charge.

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

critical mass is the minimum amount of fissionable material that must be assembled for a sustained fission reaction to take place. although two to three neutrons are produced for every fission, not all of these neutrons are available for continuing the fission reaction. if the conditions are such that the neutrons are lost at a faster rate than they are formed by fission, the chain reaction will not be self-sustaining.   at the point where the chain reaction can become self-sustaining, this is referred to as critical mass.