Select the correct alternative from the given choices. The ratio by mass of sulphur and oxygen in \(\mathrm{SO}_{2}\) is (a) \(1: 2\) (b) \(2: 1\) (c) \(1: 1\) (d) \(1: 4\)

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. By understanding stoichiometry, you can predict the amounts of substances consumed and produced in a reaction. For instance, in the exercise provided, stoichiometry helps to determine the ratio by mass of the elements in sulfur dioxide \( \mathrm{SO}_2 \). This ratio is fundamental, as it reflects the principle of the conservation of mass, where the mass of the reactants must equal the mass of the products.

The stoichiometric coefficients, derived from the chemical formula, indicate the proportion of atoms of each element in the compound. Sulfur dioxide has the formula \( \mathrm{SO}_2 \), suggesting that each molecule comprises one sulfur atom and two oxygen atoms. Hence, the stoichiometry aids in calculating the mass ratio of sulfur to oxygen, guiding us to the answer for the mass ratio problem.

The determination of molecular weight is crucial for deciphering the stoichiometry of a compound. Molecular weight, or molecular mass, is the sum of the atomic weights of all the atoms in a molecule. It's expressed in atomic mass units (amu) or grams per mole (g/mol).

In our exercise, the molecular weight calculation for sulfur dioxide involved adding the atomic weight of sulfur (32 amu) to twice the atomic weight of oxygen (2 \times 16 amu), since the molecular formula indicates twice as many oxygen atoms as sulfur. Understanding how to ascertain molecular weight enables one to further grasp how the mass of each element contributes to the overall mass of a compound, as reflected in the solution where the masses of sulfur and oxygen in \( \mathrm{SO}_2 \) were found to be equal, leading to a 1:1 mass ratio.

Chemical composition analysis involves identifying and quantifying the elements or compounds within a substance. It's a fundamental process in chemistry that assists in understanding the substance's properties, purity, and reactions it may undergo.

In the context of the exercise, chemical composition analysis allows us to dissect the compound \( \mathrm{SO}_2 \) into its constituent elements, sulfur and oxygen. By knowing the chemical composition, we can deduce the molar mass of each element and hence their proportion by mass in the compound. The calculated 1:1 ratio manifests the importance of chemical composition analysis in elucidating the characteristic ratio of elements within a molecular substance, which is essential for anyone studying or working with chemicals.