Li, C and N all three belong to the same period. They are present in the order: Li < Be < B < C < N. On moving along a period from left to right, the metallic character decreases and non-metallic character increases. So Li has the most metallic character and N has the most non- metallic character. Since metal-oxides is basic in nature, therefore oxide of Li will be most basic and non-metal oxide is acidic in nature, therefore Oxide of Nitrogen will be most acidic.