Final answer:
The correctly formatted scientific notation is option 4) 2.5 x 10^6.
Step-by-step explanation:
The correctly formatted scientific notation is option 4) 2.5 x 106. In scientific notation, the number is written as a decimal number between 1 and 10, multiplied by a power of 10. In this case, 2.5 is the decimal number, and 106 represents multiplying by 10 six times, or moving the decimal point six places to the right.