To determine which two substances are compounds, it's important to understand the definitions of elements and compounds:
- Elements are pure substances that consist of only one type of atom and cannot be broken down into simpler substances. Examples include aluminum (Al) and iron (Fe).
- Compounds are substances formed when two or more elements chemically bond together in fixed proportions. Examples include sodium chloride (NaCl) and carbon dioxide (CO2).
Now let's analyze the responses:
A. aluminum and iron - Both are elements. B. iron and sodium chloride - Iron is an element, and sodium chloride is a compound. C. carbon dioxide and aluminum - Carbon dioxide is a compound, and aluminum is an element. D. sodium chloride and carbon dioxide - Both are compounds.
The two substances that are compounds from the given options are:
D. sodium chloride and carbon dioxide.