Number of chromosomes of a monosomic individual whose 2n number is 12 will be :
11
13
12
14
As discussed in Chromosomal Number Mutations -
Aneuploidy:
In the given question,
2n = 12 Therefore, n = 12/2 which will be n = 6.
In monosomic individual, chromosomes are present in the form (2n - 1)
Therefore, (2x6 - 1) = (12 - 1) = 11
Hence, 11 number of chromosomes are present in a monosomic individual.
Hence, the correct option is (a).