Can i apply for H4 while my H1b is in RFE state right now


 Little background is like my wife got her H1B and travelling to US next week.  I have also applied for my H1b through a consultant and my H1b is in RFE state now so my question is can i apply for H4 visa .....while the H1 b is in progress.

And if yes …what should i need to explain in the interview.

One more thing i want to know…if i apply for H4 and travel on that …then what should be my next step…do i need to inform my employer to file my COS immediately or i need to wait for the approval first.