Explanation:

- Option 1: Zero

- Marginal utility is the additional satisfaction from consuming one more unit of a good.

- At the saturation point, consuming more does not increase total satisfaction.

- The additional satisfaction (marginal utility) becomes zero.

- Correct Answer

- Option 2: Unity

- Unity means the marginal utility is one.

- This implies some additional satisfaction from consumption, not correct at saturation.

- Option 3: Greater than unity

- Greater than unity implies more than one unit of satisfaction.

- This suggests increasing satisfaction, not relevant at saturation.

- Option 4: Less than unity

- Less than unity implies a positive but small increase.

- Still implies some additional satisfaction, which is not the case at saturation.