Two alleles of a gene pair are located on which among the following site of chromosome ?

Homologous sites on homologous chromosomes.

The correct answer is Option (3)- Homologous sites on homologous chromosomes .

The two alleles of a gene pair are located on "Homologous sites on homologous chromosomes."

In a diploid organism, an individual inherits one chromosome from each parent. These chromosomes are called homologous chromosomes because they carry genes for the same traits, although they may have different alleles.

The specific location on a chromosome where a gene is located is called a locus. Homologous chromosomes have corresponding loci, and the alleles of a gene pair are found at homologous sites on these chromosomes. For example, if a gene for eye color is located on a specific locus of one chromosome, the homologous chromosome will also carry a gene for eye color at the corresponding locus.

Therefore, the correct option is "Homologous sites on homologous chromosomes."