Can we opt just 100 marks (one subject of 100) from GROUP-II ???

No

__________________
In order to succeed, your desire for success should be greater than your fear of failure....

Sir what was your strategy for the subject?
kindly suggests some basic books ?

Keeping it short, Geology is a very vast field and being a Geologist my self I can understand the level of difficulty faced by the candidates, with no previous knowledge of Geology.

First of all, Geology has many branches, like too many. By looking at previous papers one can easily understand that the examiner asks questions from most of these branches. Therefore, to clear the paper one needs to have a certain level of understanding, of all the branches.

Finally! The Question is How to acquire that knowledge?

There are two strategies in my opinion: (NOTE: for people with no previous knowledge of this subject)

1. Read all the books like students of Geology do in BS. (It's a long list and kind of impractical for a number of reasons)

2. The short and time-saving method is to study one such book which summarizes all the branches of Geology. One such book is available in the market entitled "PRINCIPLES OF ENGINEERING GEOLOGY" By K.M. Bangar.

It has 12 chapters. You can leave chapter no 8, as it is about the Geology of India or more technically stratigraphy of India. You can also leave chapter number 12 as it too technical or applied you can say.

__________________
A still tongue keeps a wise head.