Guise as I am new in rc hobby can some one tell me that -
is there is any way to Charge a 4S Lipo battery with 3S Charger (B3AC COMPACT BALANCE CHARGER)??

u can't. when u open a 3S pack u will find 3 cells, when u open a 4S pack u will find four cells.
You cannot charge 4 batteries with a charging outlet for only 3 batteries.
even if you tried, it may catch fire. Buy a smart charger like :http://www.rcbazaar.com/product.aspx?productid=4076
this should help you out

If I will charge first 3 at first time and last one on latter then ...

they are all connected to the same output wire... u can seperate the 4s battery as 2 2S batteries and then connect the 2 2S batteries in series when u are using it.but be carefull not to puncture the batteries when u modify it to a 2 cell. *****USE ONLY SILICON WIRES****

hi rathi,

actualy i am new in rc hobby,

can you please make me under stand in details how i can separate the 4s battery in 2 by 2

just call me at +919591995210

dont even try that      you said u are a newbie.  so.    use a 16.8, volt smps supply and charge directly through the main output leads . this way you will'nt unbalance the lipo

I have done this previously just charge 2 cells at a time if you have a 2 cells charging socket and at regular intervals check your lipo voltage so that there is no voltage difference in cells of 2 sets.