Sahul it depends on how u solve the question..
Studying for iit doesnot mean solving 2 many questions
its actually getting thorough with the concepts, etc. if one book( i.e. study material) is sufficient then go for it..
If not then solve one more book( but not more than that). Further solving will kill ur tym.
But be through with ncerts especially chemistry..
BEST OF LUCK!!!!!!!!!!!
Plzzzz approve my answer !!!!