physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed. For example, if a piece of paper is cut up into small pieces it still is paper.
The correct answer is A. molecular formula = 2 x empirical formula
The given compound C2H10N2 is the molecular formula because the ratios of the elements are not reduced into lowest terms (empirical formula). To get the empirical formula, the ratios must be reduced to the smallest possible integral ratio which gives CH5N. As a result, the ratio between both formulas is 2.