hi,

see in case you join for individual b.sc course you would have option to select stream, college or subjects or change the subject for m.sc course. m.sc course is of 2 years, however after completing b.sc students have option to go for job or mba or msc or integrated phd course.

now coming to integrated m.sc course it also has b.sc + m.sc , but this course is research based and at the final year of b.sc i.e from third year your m.sc course would started like you may have to do research related project. there is less options to change the stream, however if you have selected in iiser or iisc like institute, I would suggest to go for it because of excellent education curriculum, thesis and research opportunity .

hope you understand.