What is the main reactant for glycolysis?

Hint: Glycolysis is a metabolic process that involves breaking down glucose into pyruvate molecules and hydrogen ions and energy. This energy is released in the form of ATP molecules, the ultimate energy currencies of the body.

Complete answer:
The main reaction of the glycolysis is given below which involves Glucose as the main reactant that leads to formation of two pyruvate molecules as products. In this reaction $NAD^+$ stands for Nicotinamide adenine dinucleotide and ADP stands for Adenosine Diphosphate. P is obviously phosphorous. All these components along with a glucose molecule undergo oxidation reaction that leads to formation pyruvate molecules, 2 ATPs ( Adenosine Triphosphate), 2 NADH ions that is, Nicotinamide Adenine Dinucleotide Hydrogen(Hydride) and independent hydrogen atoms. These ATPs are ultimately used by the body as energy currencies.
$C_6H_{12}O_6$ + 2 $NAD^+$ + 2 ADP + 2 P → 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 $H^+$
The process of glycolysis takes place in the cytoplasm or mitochondria of cells of both plants and animals. The ATP molecule released from this reaction stores the chemical energy of this reaction and eventually burns itself to fuel up any given task such as food digestion or cognition, etc. whereas the $NAD^+$ takes one hydrogen ion from glucose to form NADH. However, this NADH and Flavin Adenine Dinucleotide ($FADH_2$) transport their electrons to mitochondria to utilize their energy for further processing.

Note:
The process mentioned above is common to aerobic respirations only whereas for anaerobic process of respiration these NADH ions get dissolved to form $NAD^+$ ions in order to compensate the absence of oxygen and maintain the continuous flow of energy.