### Video Transcript

What is the mass percentage of carbon in carbon dioxide? (A) 27 percent, (B) 43 percent, (C) 44 percent, (D) 57 percent, (E) 73 percent.

Carbon dioxide is a compound, which means that it contains more than one element chemically bonded together. As a simple molecule, the formula of carbon dioxide is CO2. The formula tells us that one molecule of CO2 contains one atom of carbon and two atoms of oxygen. These atoms are bonded together by double covalent bonds between the carbon atom and the oxygen atoms.

To find the mass percentage of carbon in carbon dioxide, we need to find the percentage of the total mass of the molecule that is attributable to carbon. So, the next step is to find the molar mass of CO2, which takes into account the masses of all the atoms in the molecule. The atomic mass of carbon is about 12, and the atomic mass of oxygen is about 16. Since there’s one atom of carbon and two atoms of oxygen in carbon dioxide, the molar mass for CO2 is, therefore, 44.

12 out of 44 is the fraction of the total mass attributable to the carbon in CO2. We can simplify the fraction 12 divided by 44 by dividing the top and bottom parts of the fraction by two. Without a calculator, three divided by 11 is as far as this fraction can be simplified. But notice that three divided by 11 is slightly less than three divided by 10 numerically. Three divided by 10 equals 0.3 as a decimal. Multiplying by 100 gives us a percentage, as requested in the question. So, the answer must be a little less than 30 percent.

Since 27 percent is the only answer less than 30 percent, we can reject all the other answers which are above 30 percent. 27 percent is, therefore, the correct answer.