Directions: Read the Assertion (A) and Reason (R) carefully and choose the correct alternative. Assertion (A): A small gap is left between iron railway rails during laying of tracks. Reason (R): Iron and steel expand in hot summer and need space to expand safely.

Introduction / Context:
This Assertion and Reason question deals with thermal expansion of solids and its practical engineering application. Railways provide a classic example in physics and engineering textbooks. Metal rails experience changes in length with temperature, and engineers must account for this by leaving gaps or using special joints. The question asks whether the reason given correctly explains why small gaps are left between iron rails.

Given Data / Assumptions:

• Assertion (A): A gap is left between iron rails.
• Reason (R): Iron expands in summer.
• Rails are usually made of steel, an alloy based on iron.
• Temperature varies significantly between seasons and even within a day.

Concept / Approach:
All solids expand when heated and contract when cooled, though the amount can vary by material. Long metal structures such as rails, bridges, and pipelines can experience noticeable changes in length. If there is no room for expansion, compressive stresses build up and may cause buckling or damage. Hence, engineers design expansion joints or leave small gaps. In this question, we need to confirm that gaps are indeed left and that the stated expansion reason is correct and explanatory.

Step-by-Step Solution:
Step 1: Look at Assertion (A). Rail tracks do show visible small gaps at joints in many traditional track designs. These gaps are not accidental; they are left deliberately. Therefore Assertion (A) is true. Step 2: Reason (R) claims that iron expands in summer. Thermal expansion of metals including iron and steel is a well known physical property. When temperature increases, atomic vibrations increase and the solid expands. So Reason (R) is also true. Step 3: Rails laid in cold weather would lengthen as temperatures rise. If no gaps were left, this expansion could cause the rails to bend or buckle, creating safety hazards for trains. Step 4: By leaving small gaps between rails, engineers provide space into which each rail can expand without generating excessive compressive stress. Step 5: Thus, the Reason directly explains the purpose of the gaps mentioned in the Assertion. Without thermal expansion, such gaps would not be necessary.

Verification / Alternative check:
Physics and engineering textbooks often include diagrams showing rail joints with small clearances and explicitly state that these exist to allow for expansion in hot weather. Real world instances of track buckling during heat waves further confirm that temperature related expansion is a major design concern. This supports both the truth of Assertion (A) and the explanatory role of Reason (R).

Why Other Options Are Wrong:
Any option stating that Assertion (A) is false contradicts observations of actual rail tracks and textbook illustrations. Denying the truth of Reason (R) would go against basic principles of thermal expansion. The idea that the Reason does not explain the Assertion is also incorrect because the whole point of the gap is to accommodate expansion in hot conditions.

Common Pitfalls:
Some candidates may think the gaps are only for alignment or maintenance, forgetting the thermal aspect. Others may overlook that even small expansions, when accumulated over long lengths, can be significant. Always link examples in physics questions to the underlying physical law.

Final Answer:
Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A), so the correct option is Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).