@Mrudul instead of making it mandatory on the form, use a client script and on validateLine do your custom validation there (return false to prevent line from being committed)

with the Group Item, system would automatically explode the components one the Group Item has been added, so End of Group Line would not be initiated by user..

Ok, you would have to test exactly how that works with validateLine (does it call once for the group or for each line it's exploding etc..) but the theory should still work. Make it mandatory via script in validateLine / saveRecord instead of on the form