At night, the demand for electricity supplied by a fission nuclear reactor decreases. how is the fission nuclear reaction controlled to avoid overproduction of electricity? the temperature of the reactor is lowered because high temperature and pressure are needed. the temperature of the reactor is raised because the reaction slows down at higher temperatures. the exposure between the fuel rods and a neutron-absorbing material is increased. the exposure between the fuel rods and a neutron-absorbing material is reduced.

The correct answer is The exposure between the fuel rods and a neutron-absorbing material is increased

The only way to control or stop a nuclear chain reaction is to stop the neutrons from splitting more atoms. Control rods made of a neutron-absorbing element such as boron reduce the number of free neutrons and take them out of the reaction. These control rods are placed near the nuclear rods and they act like magnets. These control rods actually attracts the neutron and avoid them from hitting more atoms so if they are more exposed their effect will be more prominent therefore in this way the nuclear chain reaction can be controlled.

d. air pressure decreases as altitude increases.

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.