What is the fruit of wheat and rice called?

The correct option is Caryopsis.

To understand why this is the correct answer, let's break down the botanical definitions of the fruit types listed in the options:
1. Caryopsis: This is a simple, dry, one-seeded fruit in which the fruit wall (pericarp) is completely fused with the seed coat (testa). It is the characteristic fruit type of the grass family (Poaceae), which includes major cereal crops such as wheat, rice, maize, and barley. Because the seed coat and the fruit wall are inseparable, it is commonly referred to as a grain.
2. Follicle: This is a dry dehiscent fruit formed from a single carpel that splits open along only one seam (suture) at maturity to release its seeds. Examples include milkweed and peony.
3. Siliqua: This is a dry dehiscent fruit typical of the mustard family (Brassicaceae). It is formed from a bicarpellary ovary and splits along two sutures, leaving a persistent central partition (replum) to which the seeds are attached.
4. Achene: This is a dry, one-seeded indehiscent fruit where the seed is attached to the fruit wall (pericarp) by a single point or stalk (funicle), meaning the seed coat remains separate from the pericarp. Examples include sunflower seeds.

Since both wheat and rice belong to the grass family (Poaceae) and bear dry, one-seeded fruits with fused pericarp and seed coats, their fruit is botanically classified as a caryopsis.