This is not true. A square root can never be negative, thus the only answer is 4. To be precise \(\sqrt{16} = |4|\), so 4 is always positive.

Anyway you can solve the question by applying squares to both sides in order to get quantity A equal to 9 and quantity B equal to 16. Answer B is still right.

Number is already in the square root number so the number will always be positive when taken out from the root.

In the GRE when a number is under the square root in the question itself such as the one given above always take the +ve square root but if the question is such that there is no square root symbol and during the process you have to come up with a root then the root could be +ve and -ve

Many students will answer this question incorrectly because they believe that the square root of a number can be negative.
For example, some students believe that √36 = 6 or -6
However, this is not the case. The square root notation (√) tells us to identify the POSITIVE value that, when squared, equals 36

Cheers,
Brent

How is the answer A? The square root of 16 has two solutions: -4 and 4. So isn't the answer D? I'm really confused with this question.

KEEP one thing in mind, anything under the root, especially if it is a Numerical number, is always going to be positive.

Hence B.