In the given reaction:
Zn + HNO₃ → Zn(NO₃)₂ + H₂
To balance the equation, we need to consider the number of atoms on each side. The products show that each zinc (Zn) contributes to one molecule of zinc nitrate (Zn(NO₃)₂) and one molecule of hydrogen gas (H₂).
The balanced equation is:
\[ \text{Zn} + 2 \text{HNO}_3 \rightarrow \text{Zn(NO}_3)_2 + \text{H}_2\]
Here, for every zinc atom, we need 2 molecules of nitric acid (HNO₃) to produce 1 molecule of zinc nitrate (Zn(NO₃)₂) and 1 molecule of hydrogen gas (H₂).
Based on the options you've provided:
- 2HNO₃ is the correct coefficient needed for the balanced equation.
- The other options (3HNO₃, 3H₂, 2Zn, and 4H₂ and 2Zn) are not required based on the standard balancing of this reaction.
So, the coefficient that needs to be changed is 2HNO₃ (which means adding a coefficient of 2 in front of HNO₃).
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