is it possible to have 10 to the power of 2.5?
Yes; you can have 10 to an exponent of any number.
To get a decimal approximation, use a calculator; however, it can be reduced (a little):
102.5 = 102 + 0.5 = 102 x 100.5
Since 102 = 100 and 100.5 = 101/2 = √10
102.5 = 100√10