Answer:
The first option.
Step-by-step explanation:
Since these numbers are given in scientific notation, we must first look at the exponent to determine whether or not it's big or small. Negative exponents are less, so we start with that. Immediately, that eliminates the second and third options as -8 is less than -6 and 3. The last two numbers given in the first and last options, however, both have 3 as the exponent. Now, we look at the number given in front. 2.5 is less than 7, so we know that the first option is in order from least to greatest.