Do changes that cannot be easily reversed such as burning observe the law conservation of mass

Yes. Burning usually observes this kind of law.

Explanation:

The law of conversion of mass states that mass can never be formed nor can it be eradicated.

This means that in case of burning, the amount of matter before and after will remain to be the same.

It doesn't change at all.

In conclusion, there's no form of change that can be able to affect matter.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added