Question

choose all of the following that are compounds.
water (h2o)
carbon dioxide (co2)
mud
ocean water
sodium (na)
hydrogen gas (h2)
ink
air
hydrochloric acid (hcl)

Explanation:

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

• Water ($H_2O$): 2 H, 1 O → compound.
• Carbon dioxide ($CO_2$): 1 C, 2 O → compound.
• Mud: Mixture (not pure, no fixed formula) → not compound.
• Ocean water: Mixture (water + salts) → not compound.
• Sodium (Na): Single element → not compound.
• Hydrogen gas ($H_2$): Single element (diatomic) → not compound.
• Ink: Mixture → not compound.
• Air: Mixture → not compound.
• Hydrochloric acid (HCl): 1 H, 1 Cl → compound.

Answer:

• water ($H_2O$)
• carbon dioxide ($CO_2$)
• Hydrochloric acid (HCl)