QuestionClassify these substances as elements or compounds: 1. silicon (Si), 2. oxygen ($\mathrm{O}_{2}$), 3. hydrogen peroxide ($\mathrm{H}_{2} \mathrm{O}_{2}$), 4. rust ($\mathrm{Fe}_{2} \mathrm{O}_{3}$), 5. methane ($\mathrm{CH}_{4}$).

Studdy Solution
The fifth substance is methane $\left(\mathrm{CH}_{4}\right)$ in natural gas. This is a compound of carbon and hydrogen.
$$\text{Methane} \left(\mathrm{CH}_{4}\right) = \text{Compound}$$The classification is as follows1. Silicon (Si) - Element2. Oxygen ($\mathrm{}_{2}$) - Element3. Hydrogen peroxide ($\mathrm{H}_{2} \mathrm{}_{2}$) - Compound4. Rust ($\mathrm{}_{\mathrm{e}_{2}} \mathrm{}_{3}$) - Compound5. Methane ($\mathrm{CH}_{4}$) - Compound