Moderators in nuclear reactors are substances which are described by which of the following? Choose the correct answer from the options given below.

1.Which slow down the speed of neutrons

2.Which limit the chain reaction

3.Which help maintain the chain reaction

4.Without which the chain reaction would stop in most nuclear reactors

5.Such as heavy water or D2O

A1, 2, 3 and 4 only

B1, 3, 4 and 5 only ✓ Correct

C2, 3 and 4 only

D1, 2 and 5 only

Correct answer: (B) 1, 3, 4 and 5 only

Explanation

A moderator in a nuclear reactor is a substance that slows fast neutrons, sustains the chain reaction and is often heavy water, so the correct set covers these traits.

Statement 1 holds because a moderator reduces the speed of neutrons to make fission more likely.

Statement 3 holds because slowed neutrons help maintain the ongoing chain reaction.

Statement 4 holds because without a moderator most reactors would fail to sustain their chain reaction.

Statement 5 holds because heavy water and graphite are common moderators.

Statement 2 fails because limiting or controlling the chain reaction is the work of control rods, not moderators.

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