Option 1: The neutrons are made fast.

This option is incorrect. In atomic reactors, the purpose of using carbon or graphite rods as moderators is to slow down the neutrons. Fast neutrons are not desirable for sustaining a nuclear chain reaction because they have a lower probability of causing fission in the fuel atoms.

Option 2: The protons are made fast.

This option is incorrect. Protons and neutrons are both subatomic particles found in the nucleus of an atom. In nuclear reactors, the focus is on controlling neutrons, not protons. The speed of protons does not play a significant role in sustaining a nuclear chain reaction.

Option 3: The neutrons are made slow.

This option is correct. Carbon or graphite rods used in atomic reactors act as moderators, slowing down fast neutrons. Slowed down or "thermalized" neutrons have a higher probability of causing fission in the fuel atoms, which is necessary for sustaining the nuclear chain reaction.

Option 4: The protons are made slow.

This option is incorrect. As mentioned earlier, the focus in atomic reactors is on controlling the speed of neutrons, not protons. Protons are not typically manipulated or affected in the same way as neutrons in the process