Consumer surplus is the difference between the maximum amount a consumer is willing to pay for a good and the price they actually pay. It is highest in the case of luxuries, because consumers are willing to pay a lot for them even if they are not essential.
Necessities are goods that people need to survive, such as food and water. They are essential for life, so people are not willing to pay a lot for them. Comforts are goods that make life more enjoyable, but are not essential. People are willing to pay more for comforts than for necessities, but not as much as they are willing to pay for luxuries. Conventional necessities are goods that are considered to be necessary by society, even if they are not essential for survival. For example, in some cultures, owning a car is considered to be a necessity, even though it is not essential for survival. People are willing to pay more for conventional necessities than for comforts, but not as much as they are willing to pay for luxuries.
In conclusion, consumer surplus is highest in the case of luxuries, because consumers are willing to pay a lot for them even if they are not essential.