An egg cell has 10 pg of DNA in its nucleus. How much DNA will be in this animal at the end of G2-phase of mitosis?
A) 10 pg
B) 20 pg
C) 30 pg
D) 40 pg

Hint: A cell is made up of two important things, that are nucleus and the cytoplasm with cell organelles, and the nucleus of the cell contains nucleic acids, where the nucleic acid present in the animals are DNA, which is called genetic material, where all the information regarding the animal is present in its genetic material.

Complete answer:
Depending on the number of sets of chromosomes a ploidy of the cell is recommended, where a normal cell of the animals are generally diploid except for the gametes, where they contain haploid sets of chromosomes.
For example humans have 23 pairs of chromosomes, then having all chromosomes the cells of them are called diploid, and the gametes of humans such as egg or sperm they have only 23 chromosomes which means they are haploid.
So in the above given question, they said that an egg cell has 10 pg of DNA in its nucleus, so it is having only half of its chromosomes because egg is gametes.
So if the haploid cells have 10pg of DNA, normal cells have 20pg, when during mitotic division of this diploid cells, the DNA is doubled during the S phase of the mitosis, which means that it is 40pg, where S phase follows the G2 phase of the mitosis.

So, the correct option is D.

Note: Generally during mitosis cells which are produced will have same number of chromosomes to the parent cell, so to maintain it during the S phase of the mitosis, doubling of the chromosomes takes place, so later when they divide each cell has same number of chromosomes to the parent cell is present.