why is it that the square root of 16 is 4? ​

Also, if the square root is in the question the answer muct be positive.  This is by convention.

so although

\(4^2=16 \qquad    and\qquad (-4)^2=16\\~\\ \sqrt{16}=+4\)

Because: 4 x 4 =16 !!!. What number did you have in mind as the correct answer?

4²= 16 and 4*4= 16. With the commutative property of multiplication it allows you to switch the number "4" with "4". but it will still be the same answer. You can also put the equation "4*4 = 16" backwards and it will still be the same. Therefore, the square root of 16 is 4.