India Inc's operating profit margin narrowed by a sharp 2.37 per cent in the December quarter to 16.3 per cent on an annual basis due to inflation and rising energy costs, a domestic ratings agency said on Monday. When viewed sequentially, the operating profit margin for the December quarter expanded by 1.80 per cent over the preceding September quarter, Icra Ratings said, attributing the same to the easing in input costs and also price hikes by many companies.