A soap film is about 0.00000025 m thick. Which standard form matches this thickness?

The decimal point moves 7 places right to reach 2.5, so the thickness is $2.5\times 10^{-7}$ m. Stopping one place early gives $2.5\times 10^{-6}$ m, ten times too thick, and $25\times 10^{-8}$ m equals the right value but is not standard form.