Question

1. a scientist has a container with a substance inside. at first, the molecules in the substance move away from each other. later, the molecules move around each other. what change did the scientist observe in the substance?

a before, the substance was a liquid. later, it was a solid.
b before, the substance was a gas. later, it was a liquid.
c before, the substance was a liquid. later, it was a gas.
d before, the substance was a solid. later, it was a liquid.

Explanation:

To solve this, we analyze the molecular motion and states of matter:

• In a gas, molecules move far apart (away from each other).
• In a liquid, molecules move around each other (not as far apart as gas).
• In a solid, molecules vibrate in place (minimal movement).

The problem states: “At first, the molecules... move away from each other. Later, the molecules move around each other.”

• “Move away from each other” → initial state is gas.
• “Move around each other” → final state is liquid.

Now, check the options:

• Option a: Liquid → Solid (molecules in solid vibrate, not “around each other”). Eliminate.
• Option b: Gas → Liquid (matches our analysis: gas molecules move away, liquid molecules move around each other). Correct.
• Option c: Liquid → Gas (gas molecules move away (not “around”), so final state can’t be gas if motion is “around each other”). Eliminate.
• Option d: Solid → Liquid (solid molecules vibrate, not “away from each other”). Eliminate.

Answer:

b. Before, the substance was a gas. Later, it was a liquid.