hey,

the basic eligibility criteria for

1. M.S.c chemistry and joint M.S.c -Ph.D in chemistry is you must having chemistry for all three years in your graduation period and you must having mathematics in your 10+2

2. for joint M.S.c - Ph.D dual degree in environmental science and engineering , you must having any one of biology, biotechnology , chemistry, mathematics and physics for two years and any one of the other four subjects fro atleast one year in your graduation period, subject you necessary having in your 10+2 is mathematics

3. for joint M.S.c - P.h.D in atmosphere and ocean sciences , you must having mathematics and physics with any one of the these subjects among chemistry , computer science , computer application ,  geology and statistics, there is no restrictions for 10+2 subjects

kindly check according to the course you want to pursue

good luck!