(1) is the single coefficient: 1, and the degree: 2.

(2) It is a single coefficient:-1/4, and the number of times: 3 (the number of times when you can't see Y is equal to the sum of the times of X and Y)

(3) The single coefficient is -500, and the degree is 5.

(4) It is a single coefficient: 1/π, and the degree is 1.

(5) Not a monomial

(6) Not a monomial

6.A

7.C

8.D