Final answer:
In the chemical equation given, 'S' represents sulfur, making the correct answer a) Sulfur. Sulfur is involved in sulfur dioxide (SO2), where it is combined with oxygen.
Step-by-step explanation:
In the chemical equation 2Mg(s) + SO2(g) = 2MgO(s) + S(s), the 'S' represents sulfur, as indicated by the molecular formula of sulfur dioxide (SO2). Sulfur dioxide consists of sulfur and oxygen, and sulfur is the element that is missing from the left side of the equation but appears on the right side as a solid (s). Hence, the correct answer is a) Sulfur.
The student's question involves identifying the missing element in a chemical reaction equation, which is a common type of problem in stoichiometry and chemical equation balancing within the field of chemistry. The information regarding the sulfur molecule being composed of eight sulfur atoms (S8) and represented by yellow spheres in various chemical models further supports the identification of sulfur in the equation.