Best of luck with the new job. As you mentioned that currently you will receive Rs. 20K, yes, it is taxable. However, the amount of tax will depend on your salary break-up and investments as well.
Regarding the salary break-up, no one can tell you exactly what it will be, as it is finalized by the organization according to their rules.
Salary Promises and Hikes
When it comes to salary promises, I should not say, but I would still like to give you a hint that there is no organization that gives their employees such a hike within one year. I may be wrong, but based on my experience, it might not be possible. However, it does depend on your work profile and performance. Therefore, I suggest that when they finalize everything, you should ask them to mention this salary hike on your interview proforma and ensure it is written in pen, not pencil.
I hope this advice helps you, and best of luck once more. Cheers.