Directions: Read the Assertion (A) and Reason (R) carefully and choose the correct alternative. Assertion (A): In winter, a glass tumbler may crack or break if very hot water is poured into it suddenly. Reason (R): When hot water is poured into the tumbler, the outer surface of the glass expands more quickly than the inner surface.

Introduction / Context:
This question is about thermal expansion and thermal stress in materials such as glass. It uses a common household example where a glass tumbler can crack if boiling or very hot water is poured in suddenly during cold weather. The Assertion states the observed effect, while the Reason attempts to describe which part of the glass expands first. To answer correctly, we must understand how heat flows and which surface of the glass gets heated more quickly.

Given Data / Assumptions:

• Assertion (A): Glass tumbler breaks in winter when hot water is poured into it.
• Reason (R): When hot water is poured, the outer surface of glass expands.
• We assume the tumbler is initially cold, especially its outer surface due to winter conditions.
• Glass is a brittle material and does not quickly adjust to uneven expansion.

Concept / Approach:
When a hot liquid is poured into a cold glass, heat is transferred by conduction from the liquid to the inner surface of the glass. The inner surface warms up and tends to expand earlier than the outer surface, which remains relatively cold. This creates unequal expansion within the thickness of the glass. The resulting thermal stress can exceed the strength of the material, causing cracks. The Reason in the question claims the outer surface expands first, which contradicts the actual direction of heat flow.

Step-by-Step Solution:
Step 1: Consider Assertion (A). Many people have observed that thin glass tumblers may crack or shatter if very hot water is poured into them suddenly on a cold day. This is a real and common phenomenon, so Assertion (A) is true. Step 2: When hot water is poured into a cold glass, the inner surface of the glass comes into direct contact with hot water and receives heat first. Step 3: The inner surface therefore warms up, tries to expand, and experiences thermal expansion earlier than the outer surface, which is still relatively cold and contracted. Step 4: Because glass is rigid and brittle, this difference in expansion between inner and outer layers generates internal stress within the glass wall. Step 5: If the temperature difference is large and the glass is thin or flawed, the resulting stress can exceed the strength of the glass, leading to cracks or breakage. Step 6: Reason (R) states that when hot water is poured, the outer surface expands. This is incorrect: it is the inner surface that expands first. So Reason (R) is false.

Verification / Alternative check:
Thermal stress examples in physics textbooks often include the hot water in cold glass situation and clearly state that inner layers are heated first. They also note that special heat resistant glass, which tolerates larger temperature differences, is used in laboratory glassware and kitchenware to avoid such breakage. This supports the truth of the Assertion and the falsity of the specific Reason given.

Why Other Options Are Wrong:
Any option suggesting that Assertion (A) is false contradicts widely observed behaviour and textbook examples. Options that treat Reason (R) as true misrepresent the physics of heat conduction, since the side in contact with hot liquid must warm and expand first.

Common Pitfalls:
Learners may not consciously think about which surface is in contact with hot water and may assume both surfaces heat equally. Others may memorise the fact that glass breaks with sudden heating but not recall the correct direction of expansion. Always think about where heat enters a body first to decide which part expands earlier.

Final Answer:
Assertion (A) is true, but Reason (R) is false, so the correct option is Assertion (A) is true, but Reason (R) is false.