JAM

Both are better but IIT, Bombay gives better placement than IIT, Kanpur. The infrastructure of IIT, Bombay is also better and it is listed in top 10 universities of India.

Hello Dear,
There are no specific eligibility criteria up to my knowledge, You must have 50% aggregate to write for the exam.

Hello,
Yes, yes you can. IIT JAM Admission 2018 has been started from 03rd April 2018 and will end on 17th April 2018. Check the complete IIT JAM Admission Procedure here:
https://goo.gl/PX4PqC
Admission in the academic programmes will be made on the basis of the merit list of JAM 2018. Only those candidates who have cleared any one of the two test papers are eligible to apply for IIT JAM Admission in academic programmes and they must satisfy the minimum educational qualification and eligibility criteria specified by the institutes.
Best of Luck!

You need around 50 marks but it basically depends upon the difficulty level of the exam. Go for the exam with clear mindset.

No, you can't as you know you have failed in chemistry. You'll not get admission in any NIT or any B.Tech college.

Eligibility criteria:
IIT JAM 2018 Subject-wise cut-off is mentioned below. Please check, if you made the cut from the marks mentioned below. In Physics, qualifying marks for general category are 19.51 while for SC/ ST/ PWD, it is 9.76. For Physics Paper/
In Chemistry, qualifying marks for General Category students are 14.79 and 7.39 for SC/ST/PWD. For Chemistry Paper of IIT JAM 2018. In Mathematics, qualifying marks for General Category are 23.35 and 11.68 for SC/ST/PWD. Based on IIT JAM Result 2018, candidates will be admitted to institutes if they fall in above eligibility then you are eligible.
All the best.