Mathematics

The eligibility criteria of M.Sc. Mathematics of JAM 2020 is given below. Eligibility criteria : A Bachelors degree with minimum 55% aggregate marks or 5.5 CGPA/CPI out of 10 if they belong to general/OBC (NCL)/EWS category. For SC/ ST/ PwD category candidates, the eligibility criteria for the exam

For M.sc Mathematics the eligibility criteria at Lovely professional university is Pass with 55% aggregate marks in Bachelor's degree (any discipline) (with Mathematics as a subject) or B.Tech. or B.E. or B.Sc. (Engineering) or equivalent.
This is a versatile two year (four semesters) programme that

Yes there is an ews quota in DU for both PG as well as UG courses.

Stream: Astrophysics
Duration: 2 Years
Course: M.Sc. Course Type: Post Graduate
M.Sc. In Astrophysics is a full-time postgraduate course which covers both theoretical and observational aspects of astrophysics, with the course modules consisting of one compulsory module focused on building research skil

Actually you can't do like this. If you have Masters in maths then cannot go for Ph.D. in Physics without Masters in physics. Similarly you should have maths as core subject to do M.Sc. in maths. Chemistry honours students cannot do maths honours if they don't have maths.