Hello Harshita,

1. Only Past GATE Chemistry (CY) Questions (about 200-300 pages books):
   • These are good books to have, but many of these books have lots of errors and wrong answers.
   • Books written by good coaching institutes are normally more reliable than those printed by general publishing companies.
2. Theory + Questions Books (about 800-1500 pages books):

• These are not strongly recommended.
• They do not have theory in detail, and only contain brief points.
• These books could be partly useful while doing revision after complete GATE Chemistry (CY) preparation, but not good for complete comprehensive GATE Chemistry (CY) exam preparation.

Hope this helped you 

Thank you