Which of the following statements about liquids is/are true? I. Liquids maintain their volume at constant…

Analyze the question: We must decide which statements about liquids are true.

Concept: Liquids have particles that are close together but free to slide past one another. This gives them a definite volume but no definite shape. They are nearly incompressible.

Evaluate each statement:

• I. Liquids maintain their volume at constant temperature. True. A liquid has a fixed volume, whatever container it is in, as long as temperature (and pressure) stay constant.
• II. Liquids have fixed shape. False. A liquid takes the shape of its container.
• III. Liquids do not diffuse. False. Liquids do diffuse. For example, ink or potassium permanganate spreads through water, though more slowly than gases do.
• IV. Change in pressure affects the volume of liquids. Mostly false at this level. Liquids are almost incompressible, so pressure changes cause negligible change in volume. Strictly, the change is not exactly zero, but in WASSCE-level chemistry the accepted view is that liquids do not noticeably compress. Gases are the ones whose volume depends strongly on pressure.

So only statement I is true.

Answer: A. I only.

Tip: Remember the pattern for the states of matter:

• Solid: fixed shape and fixed volume
• Liquid: fixed volume, no fixed shape
• Gas: no fixed shape and no fixed volume (compressible)

Option C is the usual trap. Remember that "almost incompressible" means pressure is treated as having no effect on a liquid's volume.