Can matter be destroyed?
Matter can neither be created nor destroyed. This is the law of conservation of matter (mass).
One can prove this by performing a simple experiment at home. Fill a plastic bottle with water until it is halfway full. Now weigh it.
For example, it might be 100 g.
Now put this bottle into a freezer and let the water freeze. You may notice that after the water freezes, the bottle has expanded.
Weigh the bottle again. It will be exactly 100 g.
The amount of water (matter) stayed the same, but the volume just changed a bit.
We are really using the Law of Conservation of Mass-Energy. It states that the sum of mass and energy must always remain constant in any physical process.
In nuclear reactions, the mass of the products is less than that of the reactants. The lost mass is converted into its equivalent amount of energy according to Einstein's equation,
The total of mass-energy is the same before and after the reaction. Even though mass is not conserved, mass-energy is conserved.
The Law of Conservation of Mass works in everyday life because the energy changes are so small that we can ignore them.
For further information (incase you need/want to know it), the Law of Conservation of Mass is applied to chemical equation balancing.
Would this equation be balanced? No, because when you start out with a "something", you must end with the same amount of "something". In this case the something is O.
In this equation written above, you start out with 2 Oxygens and you end with only 1 Oxygen. So it is clear that this equation is unbalanced since it goes against the Law of Conservation of Mass (matter cannot be destroyed nor created).
So what do you do?
You balance it by adding coefficients so there would be the same amount of element on both sides.
Now if you look at the amount of each element:
H: 4 on both sides
O: 2 on both sides.
Matter was neither created nor destroyed.
(Not going to go too much in depth with equation balancing, you can find a tutorial on Socratic)
Hope it helps! Good luck!