Animated Solution for Chemistry - Solutions: A graph of vapour pressure and temperature for three different liquids X, Y, and Z is shown below : The following inference are made : A. X has higher intermolecular interactions compared to Y. B. X has lower intermolecular interactions compared to Y. C. Z has lower intermolecular interactions compared to Y. The correct inference(s) is/are :

Imagine a bustling city square where people are constantly trying to leave. In the world of chemistry, this city square is a liquid, and the people are molecules. The "vapour pressure" is essentially a measure of how successfully these molecules are escaping into the air.

But what holds them back? It's the intermolecular forces—the invisible handshakes and bonds between the molecules. If these forces are strong, the molecules are held tightly together, and very few can escape. Consequently, the vapour pressure is low. Conversely, if the intermolecular forces are weak, the molecules can easily break free, resulting in a high vapour pressure. This fundamental inverse relationship is the key to unlocking our graph.

The Vertical Slice

We are presented with a graph showing the vapour pressure of three liquids—$X$, $Y$, and $Z$—as temperature increases. To make a fair comparison, we need to level the playing field. We do this by drawing a vertical line at a constant temperature, let's call it $T_0$.

By looking at where this vertical line intersects our three curves, we can directly compare their vapour pressures under identical thermal conditions. At $T_0$, we clearly see that the vapour pressure of $X$ is the highest, followed by $Y$, and $Z$ has the lowest vapour pressure ($P_X>P_Y>P_Z$).

What does this tell us? Since liquid $X$ has the highest vapour pressure, its molecules are escaping the most easily. This implies that the intermolecular forces holding $X$ together must be the weakest. Following this logic, the strength of the intermolecular interactions follows the order: $X<Y<Z$.

The Horizontal Slice

There is another elegant way to analyze this graph: through the lens of boiling points. A liquid boils when its vapour pressure equals the surrounding atmospheric pressure.

If we draw a horizontal line representing the atmospheric pressure ($P_{\text{atm}}$), the points where it intersects the curves give us the normal boiling points of the liquids. Looking at the graph, liquid $X$ reaches this pressure at the lowest temperature, while $Z$ requires the highest temperature ($T_{b,X}<T_{b,Y}<T_{b,Z}$).

A lower boiling point means it takes less thermal energy to break the intermolecular bonds. This perfectly corroborates our previous finding: liquid $X$ has the weakest intermolecular forces, and $Z$ has the strongest.

Armed with our deduced order of intermolecular interactions ($X<Y<Z$), let's evaluate the given inferences: - Inference A: Claims $X$ has higher interactions than $Y$. This is false. - Inference B: Claims $X$ has lower interactions than $Y$. This is true. - Inference C: Claims $Z$ has lower interactions than $Y$. This is false, as $Z$ has the strongest interactions.

Therefore, the only correct inference is B, making option (b) the right answer.