Which of the following statements about compounds is true?

• A. Compounds have the same properties as the elements that form them.
• B. Compounds always exist as gases at room temperature.
• C. Compounds can be separated into their constituent elements by physical means.
• D. Compounds are substances formed by the chemical combination of two or more elements in fixed proportions.

Answer: (D)

Verified step by step guidance

1. Understand the definition of a compound: A compound is a substance formed when two or more elements chemically combine in fixed proportions.
2. Analyze the first statement: "Compounds have the same properties as the elements that form them." Consider that chemical combination changes properties, so this statement is false.
3. Analyze the second statement: "Compounds always exist as gases at room temperature." Recall that compounds can be solids, liquids, or gases at room temperature, so this statement is false.
4. Analyze the third statement: "Compounds can be separated into their constituent elements by physical means." Remember that compounds require chemical methods to separate elements, so this statement is false.
5. Confirm that the correct statement is: "Compounds are substances formed by the chemical combination of two or more elements in fixed proportions," which aligns with the definition of compounds.