Standard Form by Boxed Rockets

Are These Numbers in Standard Form?

6.02 \times 10^{-3}

Yes

2.63 \times 10^{5}

Yes

3.26 \times 10^{4}

Yes

4.57 \times 10^{-4}

Yes

63.9 \times 10^{-3}

No

0.391 \times 10^{4}

No