Gaining more marks depends on the levels of your practise because they said that nothing beats practise. But this answer is being written as to help you understand how can this book help you. Numerical Chemistry has more than 3000 numeric problems. With more than 3000 numeric problems covering each topic, Physical Chemistry book by P Bahadur provides indepth knowledge. The concepts are discussed in a simple manner but with extensive explanations and examples. If you can practise numerical concepts and revise them again atleast once or twice, this book is quite helpful. A huge no.of contents are covered in this book and each concept is solved with lot of examples. The book has a generalised format and the topics are interlinked so it is much easier for you while you are practising from it. This book is good for solving Numerical Chemistry and practise numreical concepts of Physical Chemistry. But for theory part, you may have to consider:

P.W. Atkins

O.P. Tandon

Bruce Mahan

R.C. Mukherjee

Ebbing