Hello, here I am providing you the list of the books you may refer for the IES exam for the general knowledge section as under:

An Introduction to the Constitution of India D D Basu

Perspectives on Indian Constitution Edited by Subash Kashyap

Biology for VIII-X Std NCERT

Physics for VIII-X Std NCERT

Chemistry for VIII-X Std NCERT

UPSC IES General Studies Engineering services Examinations With Solved Papers by Gkp

IES & PSU's General Studies
Publisher: Made Easy Publications

General Knowledge Manual 2012
by Barry O'Brien
Publisher: Cengage Learning India

General Studies for U.P.S.C. (IES), Public Sector (BSNL, MTNL, BHEL, DRDO, HAL, NTPC, NHPC) Other Competitive Examinations
by G K P
Publisher: G. K. Publications Pvt. Ltd

Monsoon Asia Charles Farro

Physical Geography of India for VII - XII Std NCERT

Good School Atlas:Oxford

Ancient India for VII-XII Std NCERT

Medieval India for VII-XII Std NCERT