Standard Form by Boxed Rockets

Are These Numbers in Standard Form?

0.072 \times 10^{-5}

No

3.99 \times 10^{-3}

Yes

6 \times 10^{-4}

Yes

25.4 \times 10^{6}

No

7.62 \times 10^{6}

Yes

1.1 \times 10^{6}

Yes