The correct option is B 10
The total number of chromosomes of an individual organism is called karyotype. In the question, we are given that in a particular diploid (2n) organism, the total number of chromosomes is 20. It means, the haploid number (n) would therefore be 10.
A linkage group is a group of all the genes put together which are present on a single chromosome. The number of linkage groups equals the haploid number of chromosomes present in the organism, which in this case is 10.