Coefficient 2 should be placed in the equation before the nitric acid in the reactant so that the chemical reaction becomes balanced.
The given chemical reaction is,
Zn + HNO3 --------> Zn (No3)2 + H2
Here, the elements Hydrogen, Nitrogen, and Oxygen are unbalanced.
These elements are altogether found in HNO₃ on the reactant side and are found as nitrate and hydrogen gas on the product side.
To balance the equation, the coefficient 2 is to be added in the reactant side so that 2 moles of Hydrogen, Nitrogen, and Oxygen would be balanced with 2 moles of Nitrate and two moles of Nitrogen.
On adding 2 on reactant side, we get
Zn + 2HNO3 -----------> Zn(NO3)₂ + H₂
This gives us a balanced equation and thus the equation could be balanced this way.
Therefore, coefficient 2 is to be added to make the equation to be balanced.
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