The number 4 is the square root of:

The square root of a number is a value that, when multiplied by itself, gives the original number. In this case, the number in question is 16. When you take the square root of 16, you find that 4 multiplied by 4 equals 16. Therefore, 4 is indeed the square root of 16.

For further clarity, examining the other numbers: the square roots of 12, 14, and 18 do not equal 4. For instance, the square root of 12 is approximately 3.46, the square root of 14 is approximately 3.74, and the square root of 18 is approximately 4.24. Therefore, it is accurate to state that 4 is the square root of 16, confirming that choice C is the correct answer.