is GST applicable for December 2017 attempt

Yes, GST is applicable for CS Dec 2017 exam for both executive programme as well as professional programme.
Executive programme
There is no change in the syllabus of Part A – Income Tax (70 Marks) of Tax Laws and Practice Paper (Module - 1 Paper – 4) of Executive Programme.
The syllabus for Part-B of Tax Law and Practice Paper Module - 1 Paper - 4 (30 Marks) for Executive Programme for December, 2017 exam shall be as under:
a) The Central GST Act,2017
b) The Integrated GST Act,2017
c) The Union Territory GST Act,2017
d) The GST(Compensation to States) Act,2017
The rules relating to GST regime shall not be applicable for December, 2017 exam.
[Note: Questions relating to Service Tax Laws and Value Added Tax will not be asked in December, 2017 exam.]