I gave my physics exam through NIOS , back then they use conduct twice a year but as the demand for these exams grew they started conducting on weekly bases , the same can be checked directly with NIOS or their website . Yes you can just give a single paper through NIOS ,as I had commerce in my 12th hence i had to give physics both practicals and written .
This is just one of the very STUPID and IDIOTIC rules that DGCA has but now that you have chosen to be a pilot in India then its better you get use to more and more illogical stuff to come in future.
Keep your calm , if you have passion for aviation , you will success , no DGCA ASS can ruin that .
all the best
