Question

1. choose the best answer.

compounds and their elements cannot be broken down without ______.
○ toxic results
○ releasing high quantities of heat
○ introduction of another element
○ their properties changing

1. choose all that apply.

choose three characteristics of compounds.
□ the number of elements in each molecule of a compound can be different.
□ the atoms in a compound are held tightly together.
□ compounds are rarely found on the earth.
□ elements can combine only in certain ways to form compounds.
□ different elements are chemically combined.
□ a compound must include silicon or carbon.

Explanation:

Question 3

• Option 1: toxic results – Breaking down compounds/elements doesn't inherently produce toxic results (e.g., breaking water into H and O isn't toxic). Eliminate.
• Option 2: releasing high quantities of heat – Not all breakdowns release high heat (e.g., some decompositions are endothermic). Eliminate.
• Option 3: introduction of another element – Compounds are broken down via chemical reactions (like decomposition), not by adding another element. Eliminate.
• Option 4: their properties changing – Breaking a compound (or element, though elements can't be broken into simpler substances chemically) involves a chemical change, so properties must change. For example, breaking water (a compound) into H₂ and O₂ changes its properties (water is liquid, H₂/O₂ are gases). This fits.

• 1. "The number of elements in each molecule of a compound can be different." – False. A compound has a fixed chemical formula (e.g., H₂O always has 2 H and 1 O per molecule). Eliminate.
• 2. "The atoms in a compound are held tightly together." – True. Atoms in a compound are bonded (ionic/covalent), so they're held tightly.
• 3. "Compounds are rarely found on the earth." – False. Compounds are abundant (e.g., water, CO₂, minerals). Eliminate.
• 4. "Elements can combine only in certain ways to form compounds." – True. Compounds follow fixed ratios (law of definite proportions), so elements combine in specific ways.
• 5. "Different elements are chemically combined." – True. By definition, a compound is a substance with two or more elements chemically bonded.
• 6. "A compound must include silicon or carbon." – False. Compounds can be non - carbon/silicon (e.g., H₂O, NaCl). Eliminate.

Answer:

their properties changing

Question 4