What does D represent

Why does his teacher ask him to balance the equation by including the correct coefficient

Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom? some uncharged particles are scattered by a gold foil. all uncharged particles are attracted towards a gold foil. all positively charged particles pass straight through a gold foil. some positively charged particles bounce back from a gold foil.

What is the empirical formula of c6h18o3? ch3o c2h5o c2h6o c2h5o5