In order to get admission to the MSc program of IITs, you have to appear in the IIT JAM examination. This requires BSc Hons or a major in Physics, Chemistry or Mathematics.
IGNOUs BSc major program has an option of a Physics major(48 credits of physics course out of total 96 credit for major in physics), Chemistry major(40 credits for major), Mathematics major or a BSc (General). So you can apply for IIT-JAM only if you have a
BSc major degree in Physics, Chemistry or Mathematics
BSc General degree with combinations of Physics, Chemistry and Mathematics.
You are required to necessarily have a minimum 55% aggregate in the BSc program.