Which of the statements about gases is not correct?

Analyze the question: We need the statement that is NOT correct about gases. So we test each option against what we know.

Concept: The kinetic theory of gases says:

• Gas particles are far apart, so gases have low density.
• Particles move constantly and randomly.
• Collisions between particles are perfectly elastic, so total kinetic energy is conserved.
• Gas solubility in liquids depends on temperature and pressure (Henry's law).

Checking each option:

• A. Low densities compared to solids and liquids of equal mass. Correct. For equal mass, a gas occupies a much larger volume, so its density is lower.
• B. Total kinetic energy is not affected by collision. Correct. Collisions are elastic, so kinetic energy is conserved overall.
• C. Molecules are in constant motion. Correct. This is a basic postulate of kinetic theory.
• D. Gases are highly soluble in water at high temperatures. Not correct. Dissolving a gas in water is usually exothermic. By Le Chatelier's principle, raising the temperature favours the reverse process, so the gas escapes. Gas solubility therefore decreases as temperature rises and is higher at low temperatures. This is why a warm soft drink goes flat faster than a cold one, and why fish struggle in warm water with less dissolved oxygen.

Answer: The incorrect statement is D.

Exam tip: For "gas solubility," remember: high pressure helps, high temperature hurts. Gases dissolve best in cold water under high pressure. Solid solutes like sugar are the opposite, as they usually dissolve better when hot.