A balanced chemical equation is one, in which the total mass of the reactants is equal to the total mass of the products, i.e. the total no. of atoms on the LHS is equal to the total no. of atoms on the RHS. A chem. eq. is balanced in order to make it obey the LAW OF CONSERVATION OF MASS, that states that, the total mass of products=total mass of reactants, i.e. mass is neither created nor destroyed during a chem. reaction.
This eq. is unbalanced as on LHS, total atoms=2+2=4 and on RHS=2+1=3
Let's balance it:-
Here, no. of atoms on LHS=RHS=6