You answered your own question?
Power
103 x
An exponent.
You can but it has no particular significance.
Most likely it is a logarithm.
No.
You answered your own question?
25n4
2x2x2x2x
negative 8 would be the base and the 15 would be the exponent
5de
Power
103 x
In the expression 45 the 4 is the base and the 5 is the exponent.
Then, if the exponent is a positive integer, the value is 1 multiplied by the base repeatedly, exponent times. If the exponent is a negative integer then it is the reciprocal of the above value.In either case, it is NOT the base multiplied by itself an exponent number of times.
An exponent.