Osazone formation involves only 2 carbon atoms of glucose because of:
a.) Oxidation
b.) Chelation
c.) Reduction
d.) hydrolysis

Hint: Osazone are a class of carbohydrate derivatives which formed when reducing sugars are reacted with excess of phenylhydrazine at boiling temperatures i.e. the formation of Osazone involves reduction of phenyl hydrazine.

Complete step by step answer:
 Oxidation is the process of gaining of oxygen and removal of hydrogen whereas Reduction is the process of removal of Oxygen and gaining of Hydrogen.
Chelation is a type of bonding of ions and molecules to metal ions which involves the formation or presence of two or more separate coordinate bonds between a polydentate ligand and central metal atom.
Mechanism of the formation of glucosazone would help us reveal the solution.
When D-glucose is added to phenylhydrazine, it reacts with one molecule of phenyl hydrazine to form D-glucose phenyl hydrazone. Second molecule of phenyl hydrazine then oxidizes the second Carbon atom from alcohol to the keto group and the Third molecule of phenyl hydrazine reacts to form D-glucosazone.
So, the correct answer is “Option B”.

Note: While going through the given reaction of formation of Glucosazone, one must remember that the reaction involves formation of a pair of phenylhydrazone functional group accompanying the oxidation of the hydroxyl group on the $\alpha -Carbon$ i.e. the carbon atom adjacent to the carbonyl center of the glucose molecule.