My conditional greencard expaired and filed for permanant greencard(I-751)but planning to go to india how?

When you filed your I-751 you should have received a receipt notice that indicated that work authorization and travel approved. In order to return to the U.S. from travel abroad you will need this original receipt notice and your expired conditional green card. However, remember that you will likely be required to attend an interview on the I-751 petition so you need to take this into consideration when planning your trip abroad.