After wood burns, the ash weighs much less than the original wood. explain why the law of conservation of mass is not violated in this situation

When wood burns it makes 1 ash and 2 CO and so law of conversation matter wouldn't be violated as the ash + the smoke each would have a fraction of the original matter from the wood

The law of conservation of mass is not violated for a couple of reasons. The first reason is that weight and mass are not the same thing. Weight is the amount of gravity pulling on an object, whereas mass is the amount of space that an object takes up or the amount of matter that the object has. The other reason is that just because the wood was burned, the mass was not destroyed. Part of the wood burned became ash, but all that happened was the atoms in the wood being rearranged. They were not destroyed.