Which of the following expressions is written in scientific notation?

a. 0.3 x 104
b. 2 x 10-5
c. 10 x 103
d. 12 x 10-3

The most important requirement for an expression to be a scientific notation is that the whole number is between 1 and 10, but not including 10.
So, having this in mind, the correct answer has to be B. 2 x 10-5, because 2 is the only number between 1 and 10 here.

B. because it is the only one that makes enough sense

Ais right if u want more just write the common factors (the numbers that you multiply)