Answer:
Option B, Increase the unsystematic risk of the portfolio, is the right answer.
Explanation:
Option B is correct because unsystematic risk refers to the risk that can be reduced drastically by diversifying the investment or portfolio. A company can reduce such risk by investing in a large range of projects or in large companies. Therefore, if the diversification decreases, as we can see in the question that the stock portfolio decreased from 50 to 10 then the unsystematic risk will increase.