Answer: A chemical equation can be defined as balanced chemical equation if the number of atoms and the total charge is same on both sides of the reaction i.e reactants and products have same number of atoms.
Whereas, imbalanced reaction does not have same number of atoms and charge on reactants and products.
A. 2CO + 2NO → 2CO2 + N2 is a balanced equation as the number of carbon, oxygen, and nitrogen atoms are same on both sides.
B. 6CO2 + 6H2O → C6H12O6 + O2 is an imbalanced equation as oxygen atoms are not balanced here.
C. H2CO3 → H2O + CO2 is a balanced equation as same number of hydrogen, carbon, and oxygen are present on both sides.
D. 2Cu + O2 → CuO is an imbalanced equation as both copper and oxygen are imbalanced here.