What is the correct way to write 0.0000250 m in scientific notation?

Your answer to this is 

2.5×10−5

Move the decimal so there is one non-zero digit to the left of the decimal point.
 
The number of decimal places you move will be the exponent on the 1010.
 
If the decimal is being moved to the right, the exponent will be negative.
 
If the decimal is being moved to the left, the exponent will be positive.

2.5^-0.4 would be correct

Ithink this is what you meant. the temperature at which a liquid begins to boil is called the boiling point. the boiling point of water is 212°f or 100°c.  and at that point will start to turn into steam (gas)