Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason

Q: Why does a liquid want to minimize its surface area?

Molecules at the surface of a liquid experience a net inward pull because they don't have identical molecules above them. This inward force creates surface tension, making the liquid behave like a stretched elastic membrane that tries to shrink to the smallest possible area.

Q: What is the exact difference between surface tension and viscosity?

Surface tension is a static property that dictates the *shape* a liquid takes to minimize energy (like forming a drop). Viscosity is a dynamic property that dictates how *fast* or easily the liquid flows when a force is applied.

Q: Does viscosity really decrease when we heat glass?

Yes! Heating provides thermal energy to the molecules. They vibrate more vigorously, which helps them overcome the intermolecular attractive forces holding them together. This makes it easier for layers of the liquid to slide past one another, meaning lower viscosity.

Q: Why doesn't the glass just drip down when heated?

Even though the viscosity decreases upon melting, molten glass is still incredibly viscous compared to water. It flows very slowly. Before it has a chance to drip, surface tension quickly rounds off the edges, and we remove the heat to solidify it again.

Q: Is glass considered a solid or a supercooled liquid?

Glass is an amorphous solid. While it lacks the long-range ordered crystalline structure of typical solids, its molecules are locked in place at room temperature. The old myth that glass is a 'supercooled liquid' that flows over centuries is actually false!

Question

Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) Sharp glass edge becomes smooth on heating it upto its melting point.
Reason (R) The viscosity of glass decreases on melting.
Choose the most appropriate answer from the options given below.

Options:

(A) A is true but R is false

(B) Both A and R are true but R is not the correct explanation of A.

(C) A is false but R is true.

(D) Both A and R are true and R is the correct explanation of A.

Sigma Percentile · Accepted Answer

### The Danger of Sharp Edges
Imagine you are working in a chemistry laboratory, and you accidentally break a glass rod. The resulting edge is incredibly sharp, jagged, and dangerous. To make it safe to handle, chemists use a technique called **fire polishing**. The assertion in our problem states that when we heat this sharp glass edge up to its melting point, it magically becomes smooth. But what is the actual physics behind this transformation?

### The Heat is On
When we place the jagged edge of the glass rod into the hot flame of a Bunsen burner, the thermal energy begins to break down the rigid intermolecular bonds of the solid glass. The glass transitions from a solid state into a highly viscous liquid state.

At this point, the Reason (R) statement comes into play. It claims that the viscosity of glass decreases on melting. This is a fundamental truth of thermodynamics. As the temperature increases ($T \uparrow$), the kinetic energy of the molecules also increases. This vigorous molecular vibration overcomes the attractive intermolecular forces, allowing the layers of molten glass to slide past one another more easily. Consequently, the viscosity drops ($\eta \downarrow$).

### The Invisible Hand of Surface Tension
So, we have established that both the Assertion (A) and the Reason (R) are factually correct statements. But here is the critical catch: is the drop in viscosity the *reason* the glass becomes smooth?

Absolutely not! The true hero of this story is **Surface Tension**. Every liquid possesses surface tension, a property that drives it to minimize its exposed surface area. Molecules at the surface experience a net inward pull, acting like a stretched elastic membrane. Geometrically, a curved or spherical shape provides the absolute minimum surface area for any given volume.

### The Final Verdict
While the decrease in viscosity allows the molten glass to flow, it is the surface tension that actively pulls the jagged, high-surface-area spikes into a smooth, low-surface-area rounded curve. Therefore, while both statements are true, the decrease in viscosity is merely a facilitator, not the driving force. The correct explanation for the smoothing of the glass is surface tension, meaning Reason (R) is **not** the correct explanation for Assertion (A).

Select Answer:

Visualized Solution

$A sser t i o n (A)$

$H e a t in g t h e Gl a ss$

$R o l e o f S u r f a ce T e n s i o n$

$R e a so n (R)$

$C o n c l u s i o n$

The Sigma Insight: Liquid State

The Danger of Sharp Edges Imagine you are working in a chemistry laboratory, and you accidentally break a glass rod

The Heat is On When we place the jagged edge of the glass rod into the hot flame of a Bunsen burner, the thermal energy begins to break down the rigid intermolecular bonds of the solid glass

The Invisible Hand of Surface Tension So, we have established that both the Assertion (A) and the Reason (R) are factually correct statements

The Final Verdict While the decrease in viscosity allows the molten glass to flow, it is the surface tension that actively pulls the jagged, high-surface-area spikes into a smooth, low-surface-area rounded curve

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The relative strength of interionic/intermolecular forces in decreasing order is