Which of the following is not a polynomial?

A polynomial is an expression consisting of variables and coefficients, that involves only the operations of addition, subtraction, multiplication, and non-negative exponents of variables.

In x² + 1/x² – 4, there is a negative exponent – 2 to x. So this is not a polynomial.

Hence, option(C) is the correct one i.e. x2 + 1/x2 – 4