Final answer:
The black residue on a charred candle wick is primarily composed of carbon, an essential component of all living matter and fossil fuels. This is due to incomplete combustion, where carbon is left as a residue.
Step-by-step explanation:
The black material on a charred candle wick is primarily composed of the element carbon. Carbon is a crucial component of all living matter, including plants, animals, and humans, and it makes up a significant part of fossil fuels such as coal, oil, and natural gas. In the instance of a candle wick, when the wax (which is also a carbon compound) burns incompletely, it leaves behind carbon in the form of black soot. This is a common form of elemental carbon. The other elements listed as options (oxygen, hydrogen, and nitrogen) also play vital roles in living organisms, but the charred remains of a wick are predominantly carbon.
Carbon's versatility allows it to form a variety of compounds and exist in several allotropes, such as graphite, diamond, and amorphous carbon. In the combustion process, if there is insufficient oxygen, as is the case with a candle wick, complete combustion does not occur, and the element carbon is left as a residue in the form of black soot or char. This is indicative of the carbon's incomplete oxidation. This black residue's composition is similar to other forms of elemental carbon such as carbon black, charcoal, and coke.