Solution:Concept- A balanced chemical equation is the equation which has the equal number of atoms present on both sides of the equation.
Thus, to balance the equation, we keep the count of the elements balanced on both sides of the reaction which maintains the same total mass of elements on both sides. Also , the charges should also remain the same on both sides.
Now, the unbalanced chemical reaction :
Now, balancing the H and O atoms:
Now, balance the Cu and N atoms according to its oxidation state:
Hence, the correct answer is 1.