Which principle to explain the reason behind why the two alleles for a single trait separate from each other when gametes are made, allowing to ensure that each gamete only carries one allele?

The law of A. segregation is the Mendel’s laws or principles explain that traits are passed from parents to offspring individually instead of as pairs, groups or sets. So the correct option is option “A” as far as the given question is concerned. This is a law or principle which states that during the formation of gametes, two copies of each heredity factors separate out so that the new offspring can get one factor of both the parents. This law was the first law in this direction.