Answer: C. Metaphase of mitosis.
Step-by-step explanation : 
- A karyotype of a person reveals the number and the structure of the chromosomes present in his cell. 
 
- For making a karyotype a somatic cell is chosen which is arrested in the metaphase stage of mitosis.
 
- The metaphase stage of mitosis is chosen because at this stage:
 
A) A complete set of chromosomes is present (cell is diploid).
B) The chromosomes are most condensed at this stage. 
- Due to these reasons, the metaphase stage is selected to prepare a karyotype.