Standard Form by Boxed Rockets

Are These Numbers in Standard Form?

6.97 \times 10^{-6}

Yes

2.25 \times 10^{-5}

Yes

8.26 \times 10^{-4}

Yes

7.2 \times 10^{6}

Yes

18.5 \times 10^{6}

No

7.6 \times 10^{-4}

Yes