In groundnut, oil is stored in EdospermsCotyledons Fruit Pericarp Scutellum

Hai Kajol garg,
Ground nut is an legume plant where the fruit is present in the soil.
The answer for your question is cotyledon because it is the storage material that stores food substances.

To answer this question remember the parts of a fruit.
Endosprem-part of seed which is storage in function found only in monocots.
Cotyledon- food storage material (seed)
Fruit- Whole fruit
Pericarp- Outer layer of fruit
Scutellum- Layer that protects the developing new plant parts radicle and plumule

Also look into the below two images for through understanding