Question

figure 1
which one of the following statements are true of the sample of matter described by figure 1?
○ as heat is added to the sample, its temperature always increases.
○ the sample is melting between a temperature of about -100°c and -10°c.
○ the liquid state would be observed in the sample at both 200 seconds and 400 seconds.
○ the solid state would be observed in the sample at both 600 seconds and 800 seconds.

Explanation:

Step1: Analyze Option 1

In a heating curve (like Figure 1), during phase changes (melting, boiling), heat is added but temperature remains constant (the flat parts of the graph). So the statement "As heat is added to the sample, its temperature always increases" is false because there are flat segments (e.g., between A - B, B - C? Wait, no, looking at the graph: A to B? Wait, the graph has flat parts at B (around 0°C, maybe melting) and D (around 200°C? Wait, no, the y - axis is temperature. Let's re - examine: the first flat part is around 0°C (from ~150 to 350 seconds maybe), then a rise, then another flat part around 200°C (from ~500 to 750 seconds). So when heat is added during these flat parts, temperature doesn't increase. So Option 1 is false.

Step2: Analyze Option 2

Melting occurs at the first flat part of the heating curve (where temperature is constant while solid turns to liquid). Looking at the graph, the first flat part is around 0°C (not - 100°C to - 10°C). The temperature at point A is around - 100°C to - 10°C? Wait, point A is at ~50 seconds, temperature ~ - 50°C? Wait, the y - axis: 0 is in the middle, below is negative, above is positive. The first flat part is around 0°C (the horizontal line at y = 0, from x = 150 to x = 350 maybe). So melting is at 0°C, not - 100 to - 10. So Option 2 is false.

Step3: Analyze Option 3

At 200 seconds: the graph is at the first flat part (melting phase), so the sample is melting (solid and liquid co - exist? Wait, no, during melting, solid is turning to liquid. Wait, at 200 seconds, it's in the melting phase (flat line, temperature constant), so there is liquid (since melting is solid to liquid). At 400 seconds: after the first flat part, the temperature is rising, so the sample is in liquid state (since melting is complete, and now heating the liquid). So at 200 seconds (melting, so liquid present) and 400 seconds (liquid, heating), so liquid state is observed at both. Let's check other options to be sure.

Step4: Analyze Option 4

At 600 seconds: the sample is at the second flat part (boiling? Or maybe vaporization? Wait, the second flat part is around 200°C, so it's the boiling phase (liquid to gas). So at 600 seconds, the sample is in the process of boiling (liquid and gas co - exist). At 800 seconds: after the second flat part, the temperature is rising, so it's in gas state? Wait, no, after the second flat part (boiling), when the flat part ends (at ~750 seconds), the temperature starts to rise, so at 800 seconds, it's in gas state. So at 600 seconds, it's liquid - gas co - exist, at 800 seconds, gas. So solid state is not observed at 600 or 800 seconds. So Option 4 is false.

Answer:

The sample is melting between a temperature of about - 100°C and - 10°C. (Wait, no, earlier analysis was wrong. Wait, maybe I misread the graph. Wait, the first point A is at (50, - 50), then the line goes up to a flat line at y = 0 (temperature 0°C) from x = 150 to x = 350 (point B is at x = 200, y = 0). Then it goes up to point C (x = 450, y = 100), then up to a flat line at y = 200 (point D at x = 700, y = 200), then up to E. So:

• Option 1: False, because during flat parts (melting and boiling), temperature doesn't increase.

• Option 2: The first flat part (melting) is at 0°C, not - 100 to - 10. False.

• Option 3: At 200s: in melting phase (y = 0, flat line), so liquid is present (melting is solid to liquid, so liquid exists). At 400s: after melting (the flat line ended at x = 350), so from x = 350 to x = 500, temperature is rising (liquid being heated). So at 400s, it's liquid. So liquid at both 200s and 400s.

• Option 4: At 600s: in the second flat part (boiling, y = 200°C), so liquid and gas co - exist. At 800s: after the second flat part (ended at x = 750), temperature is rising, so gas. So solid is not present at 600s or 800s. So Option 3 is true.

So the correct statement is "The liquid state would be observed in the sample at both 200 seconds and 400 seconds."