Which one of the following is a true nut?
(A)Hazelnut
(B)Groundnut
(C)Cashewnut
(D)Coconut

Hint: A nut is a fruit composed of an inedible hard shell and a commonly edible grain. In common usage and a cooking sense, a broad variety of scorched seeds are called nuts, but in a botanical context "nut" indicates that the shell does not open to disclose the seed.

Complete answer:
Option (A)Hazelnut
A true nut is a fruit that seems like a hard shell and an edible seed. The shell does not open to disclose the seed (indehiscent), e.g., hazelnut, chestnuts.
It also is noticed as a cobnut or filbert nut according to species. The seed has a narrow, dark brown skin, which is periodically removed before cooking. Hazelnuts are healthy in protein, fat, vitamin E, manganese, and various significant nutrients.
Hazelnuts are true nuts. The fruit originates from a compound ovary and does not open to release its single seed. Many nutritive oily seeds are popularly named “nuts,” particularly those with a hard shell.

Option (B)Groundnut
The groundnut or peanut is not a true nut, but relatively a legume. In groundnut, edible cotyledons stay below ground and act as a depository organ. So this option is not correct.

Option (C)Cashewnut
Cashew nuts are not true nuts. In the cashew nut, the ovary evolves outside of the fruit that is like false fruit. Therefore, this option is not correct.

Option (D)Coconut
The fruit of the coconut is a huge, dry drupe. So this option is not correct.

Hence the correct answer is OPTION(A)

Note: A true nut, biologically reciting, is a hard-shelled pod that includes both the fruit and seed of the plant, where the fruit does not unwrap to release the seed. Nuts are characterized as a simple, dry fruit with one seed (sometimes two) in which the seed case wall comes to be very hard at maturity