How many significant figures?
It is ambiguous. 2500 can either be 2.5E3 or 2.500E3. The number 2506 would clearly be 2.506E3. Changes of last two digits being zeros randomly is 1%. If this is a home question or on a test then work the answer to 4 figures state that the problems seems ambiguous and that your assumption is that there are only two significant figures in the given temperature and round your answer to 1.6E3.

I'll point out that your answer has the same ambiguity. Is 1600 really 1.6E3 or 1.600E3?