Answer:
1, 2, 3
Explanation:
Using a simple chemical reaction as an example;
2H2 + O2 --> 2H2O
1) number of atoms
In the reactant side (left side of the reaction), there are 4 Hydrogen atoms which is equal with the number of atoms in the product (right side of the reaction). In the reactant side, there are 2 oxygen atoms, same thing with the product side. This means it is conserved.
2) Number of electrons
The number of electrons are also balanced. Although there is sharing of electrons, This means it is conserved.
3) In a chemical reaction, the law of conservation of matter is obeyed. Since the number of atoms is conserved, the mass is also conserved.
4) numbers of molecules
Although this is true for some reactions, it is not always the case as seen in the reaction above. This means it is not conserved.
