The ploidy level of primary endosperm nucleus in Oenothera before fertilisation is
A) n
B) 3n
C) 2n
D) 5n

Hint: The complete set of chromosomes in a cell and the number of possible alleles is known as ploidy. It is the number giver for the autosomal or pseudoautosomal genes. Mostly, all sexually reproducing organisms are diploid or polyploid.

Complete answer: The primary endosperm nucleus is the nucleus formed by the fusion of two polar nuclei in the embryo sac of an angiosperm plant before fertilisation. Oenothera is a herbaceous flowering plant. In the endosperm, the central egg cell has n chromosomes contributed by the mother. After fertilisation, the cell or the zygote becomes a diploid endosperm after receiving the contribution from the father. Thus, ploidy is 2n. Humans contain 2n chromosomes, where n=23 from father and n=23 from mother. The number of chromosomes in Oenothera is 14. In somatic cells, the chromosomes exist in pairs. This is known as diploidy. When meiosis takes place, the cell produces gametes. The gametes contain half the number of chromosomes. This is called haploidy. The diploid condition is restored when two germ cells unite.
Thus, the correct answer is option C.

Note: The polyploid condition occurs in plants which is the result of chromosome duplication without the division of cytoplasm or without fertilisation. The cell with an abnormal number of chromosomes is called aneuploidy. It results in an unequal distribution of chromosomes in the daughter cells.