Following is the books list for chemistry optional which i got from Abhijet Aggarwal's interview (CSE-2009,AIR-25) having chemistry and Physics as optional:-

• Physical chem by Puri Sharma and Pathania
• Phy chemistry by castellan
• Phy chemistry by Atkins
• Chemical Kinectics - Laider
• Selected topics in inorganic chemistry - Tuli and Madan
• Inorganic chemisty- Puri sharma and kaila(PSK)
• Inorganic chemistry, Principle, structure and Reactivity - Huheey
• Inorg chemistry - J.D. Lee
• Organic Chemistry - Mcmurry, Morrison and Boyed, Peter Sykes and R.K. Bansal
• Photochemistry and pericyclic reactions by Jaya singh and Jagdamba singh
• Spectroscopy -Y.R.Sharma, P.S.Kals, william kemp , Donald Pavia.

These are the books from the article.
 
Thanks
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Simranjit Singh, IAS Aspirant