Question

which of these is a compound? a salt (nacl) b gold (au) c helium (he) d oxygen gas (o₂)

Explanation:

A compound is a substance made of two or more different elements chemically bonded.

• Option A: Salt (NaCl) has sodium (Na) and chlorine (Cl), different elements bonded → compound.
• Option B: Gold (Au) is a single element → element, not compound.
• Option C: Helium (He) is a single element → element, not compound.
• Option D: Oxygen gas (O₂) has only oxygen → element (diatomic), not compound.

Answer:

A. Salt (NaCl)