Which one of the following is incorrect?
1. | A chemical equation is balanced in the sense that the number of atoms of each element is the same on both sides of the equation. |
2. | The number of atoms of each element is not necessarily conserved in a nuclear reaction. |
3. | The number of protons and the number of neutrons are conserved in each nuclear reaction. |
4. | Mass-energy interconversion takes place only in nuclear reactions and never in the chemical reaction. |