Directions: For the Assertion (A) and Reason (R) given below, choose the correct alternative. Assertion (A): Carbon dioxide turns lime water milky. Reason (R): Carbon dioxide makes the water dirty.

Introduction / Context:
This question is from basic chemistry and concerns a very common test for carbon dioxide gas. Passing carbon dioxide through lime water is a standard experiment in school laboratories. The assertion–reason format is used to test whether students know both the observable effect and the correct scientific reason behind it.

Given Data / Assumptions:

• Assertion (A): Carbon dioxide turns lime water milky.
• Reason (R): Carbon dioxide makes the water dirty.
• We assume school level chemistry content on lime water and gases.
• The problem is to evaluate both statements and check the explanation.

Concept / Approach:
Lime water is a dilute solution of calcium hydroxide. When carbon dioxide gas is passed through lime water, a chemical reaction occurs producing calcium carbonate, which is insoluble and appears as a white precipitate. This white solid gives the solution a milky or cloudy appearance. The correct explanation is therefore based on formation of an insoluble compound, not on any idea of dirtiness.

Step-by-Step Solution:
Step 1: Evaluate Assertion (A). The observation that carbon dioxide turns lime water milky is a standard textbook fact and is used as a test to detect the presence of carbon dioxide gas. So A is true.Step 2: Evaluate Reason (R). The statement says that carbon dioxide makes the water dirty. This is not a scientific explanation. The milky appearance is not due to dirt but due to a specific chemical reaction and formation of a precipitate.Step 3: The chemical reaction is: calcium hydroxide solution reacts with carbon dioxide to form calcium carbonate and water. Calcium carbonate is insoluble and appears as fine white solid particles suspended in the liquid, which scatter light and give the milky look.Step 4: Therefore R is false as it describes the effect using an incorrect idea of dirtiness rather than the true cause, which is precipitation of calcium carbonate.Step 5: Since A is true and R is false, the correct option is that A is true but R is false.

Verification / Alternative check:
If simple dirtiness were the cause, then any gas or substance that made water dirty would give a similar milky result, which is not the case. Also, once the precipitate settles, the upper part of the liquid can become clearer again, showing that the cloudiness was due to suspended solid particles. This behaviour matches the chemical explanation, not a vague idea of dirt.

Why Other Options Are Wrong:
Option a treats the incorrect statement about dirt as a true explanation, which is scientifically wrong. Option b assumes R is true but not explanatory, which also fails. Option d requires A to be false, which contradicts widely repeated experimental observations about lime water and carbon dioxide.

Common Pitfalls:
Students may repeat informal language such as “the water becomes dirty” without understanding the underlying chemistry. In exams, it is important to translate everyday descriptions into proper scientific explanations involving reactions and precipitates, especially for commonly taught tests like the lime water test for carbon dioxide.

Final Answer:
The correct evaluation is that Assertion (A) is true but Reason (R) is false.