From the graph, it can be inferred that

This question tests the ability to read and interpret a solubility-temperature graph. The graph plots solubility (y-axis) against temperature in °C (x-axis) for four substances: X, Y, Z, and Q.

Examining each curve on the graph:

• X shows a steep, curved increase in solubility with temperature. Its solubility rises slowly at lower temperatures but accelerates sharply at higher temperatures, giving a concave-upward curve.
• Y follows a straight line from the origin, rising at a constant rate as temperature increases. This is a steady, linear increase in solubility.
• Z appears as a nearly horizontal line at about 45 units of solubility, meaning its solubility barely changes regardless of temperature. Z is essentially temperature-independent.
• Q rises to a peak around 40 to 50 °C and then decreases, meaning its solubility first increases and then drops with further heating.

The correct inference is that the solubility of Y increases steadily as temperature increases. The word "steadily" is key here: Y's straight-line graph means its solubility rises at a uniform, constant rate per degree of temperature increase. X also increases with temperature, but its increase is not steady; it accelerates (curves upward), so the rate of increase itself changes.

The claim that the solubility of X and Y is the same at all temperatures is incorrect because the two curves only intersect at a single point; at all other temperatures, their solubilities differ. The claim that the solubility of X, Y, and Z is temperature dependent is incorrect because Z is nearly flat, showing its solubility is essentially independent of temperature. The claim that the solubility of Z increases as temperature increases is directly contradicted by Z's horizontal line on the graph.

Exam tip: When a question uses the word "steadily," look for a straight-line relationship on the graph. A curve that bends upward or downward represents a changing rate of increase, not a steady one.