None of these are true roots.
a. The closest true root to √50 is 7.
7^2 = 49
b. The closest true root to √150 is 12.
12^2 = 144
c. The closest true root to √350 is 19.
19^2 = 361
d. This is a cubed root, rather than a square root.
The closest root to 3√350 is 7.
7^3 = 343