Which of the following is not a step in the conversion of 25 L to hm^3

However, it is really a bad question for two reasons. First, hektometers is a unit which is never used. Second, you can do the conversion without using any of those conversion factors, viz:

25L (10^-3 m^3 / L) (1 hm^3 / 100^3 m^3) = (25) (10^-3) / (10^6) hm^3 = 25 * 10^-9 hm^3

so you could argue that any of the choices is a correct answer.