Which statement summarizes the law of segregation?

gametes are passed in pairs, groups, or sets.
traits that are dominant mask traits that are recessive.
gametes carry one allele for each trait.
traits are passed independently of one another.

The correct statement that summarizes the law of segregation is that gametes carry one allele for each trait.  

The guidelines, which govern heredity were identified by a monk named Gregor Mendel in the 1860s. One of the principles, also known as Mendel's law of segregation, suggests that the pairs of alleles segregate or separate at the time of gamete formation, and arbitrarily unite at the time of fertilization.  

The correct answer is- Gametes carry one allele for each trait.

Gamete ( also called sex cell or reproductive cell) is a haploid cell that is produced through a cell division, termed as meiosis in the sexually reproducing organisms.

According to the law of segregation ( which is second law of inheritance) given by Gregor Mendel-

For every characteristic/ trait of an organism, there are two variant forms ( dominant and recessive) of a gene, called alleles. They are separated from one another so that every gamete possesses one allele. This law is also known as law of purity of gametes.

Thus, first statement summarizes the law of segregation.