explain the calculation for me. Thks u

You are planning to invest in a two-asset portfolio and you would like to get the greatest possible reduction in unsystematic risk. Which of the following correlation coefficients should you be trying to achieve between the two assets? Select one: a. 0 b. 1 c. 2 d. 3 The correct answer is -1 Which of the following would be the best number of stocks in a portfolio if you want to eliminate the majority of the unsystematic risk without incurring excessive transaction costs? a. 110 b. 4 c. 54 d. 20