Square is an operation that involves multiplying a number by itself. It is denoted by placing a superscript 2 after the number. For example, squaring the number 3 would result in 3^2 = 9.

The inverse operation of square is called the square root. The square root is the value that, when multiplied by itself, gives the original number. It is denoted by the symbol √. For example, the square root of 9 is √9 = 3.

Now, let's discuss each option to see if it is the inverse operation of square or not.

a) Square root: As mentioned above, the square root is indeed the inverse operation of square. It "undoes" the squaring operation by finding the original number. For any positive number x, taking the square root of x and then squaring the result will give back the original number x.

b) Cube root: The cube root is not the inverse operation of square. The cube root of a number x is the value that, when multiplied by itself three times, gives the original number. It is denoted by the symbol ∛. The cube root is related to the operation of cubing, which involves multiplying a number by itself three times.

c) Square: The square operation itself is not its own inverse. Squaring a number and then squaring the result will not give back the original number. For example, squaring 2 gives 4, but squaring 4 gives 16, not 2.

d) None of these: This option is incorrect because the inverse operation of square is indeed the square root.

In conclusion, the correct answer is option a) Square root, as it is the inverse operation of square. The square root undoes the squaring operation by finding the original number.