The answers are the following:
1. 4.8x100^7 is not in scientific notation.
No; it is not written as a number times a power of 10. It should not be "times 100" because in scientific notation, the highest number to be expanded by the degree is 10.
2. 5.1x10^-8 is in scientific notation.
yes; the number is written in scienfic notation. This is because it has a base number and multiply to x10^-8 which is the exponent indicating that the expanded value is 0.000000051