Answer: the correct answer for the fill in the blank is Pyruvic acid.
Glycolysis is a metabolic process, which includes the breakdown of glucose ( a simple sugar) into 2 molecules of pyruvate ( a two carbon containing compound) or pyruvic acid with the formation of net 2 ATP and 2 NADH.
It is therefore a pathway for extracting energy from glucose. It occurs in the cytoplasm of all living cells.
Thus, glycolysis ends in the production of pyruvic acid.