Why does burning wood leaves an ash that is only a small fraction of the mass of the original wood.?

Explanation:

Burning wood leaves an ash which is a small amount of original mass of wood because when we burn wood, large amount of wood is converted into carbon dioxide and water vapor. In complete combustion, there would be no ash remaining, because all the fuel have been consumed completely. When we sum up the mass of gasses released in burning and the ashes we get the original mass.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

on passing the small ampere of electric current through the tube made of ar and hg of cfl generates uv rays which excites the fluorescent and thus emits the high radiation by consumption of just 5- 12 w in comparison to incandescent light which requires more power such as around 40 - 55 w to lighten.

moreover the life span of fluorescent or cfl is around 8000 h whereas the life span of incandescent is around 1200 h

hence, the building installed with incandescent lights bears more electricity bill.