Is the square root of 16 a rational or an irrational number?

sqrt(16) = +/- 3

Both +4 & -4 are rational.

NB The square roots of prime numbers are irrational

e.g. sqrt(2) = 1.413213562....

sqrt(3) = 1.732050808....

sqrt(5) = 2.236067978....

et seq.,