Exponent is a number used to express shorter equation; it is a number that says how many times you are going to multiply the base number.
Exponents have several laws, here are some:
=> x^1 = x
=> x^0 = 1
=> x^-1 = 1/x
=> x^m x^n = X^m+n
=> x^m/x^n = x^m-n
And since we were asked to write an expression with a negative exponent that has a value between 0 and ½
=> 2^ -2 = ½