Directions: For the Assertion (A) and Reason (R) below, choose the correct alternative. Assertion (A): Pluto is the coldest planet. Reason (R): It receives slanting rays of the sun.

Introduction / Context:
This Assertion and Reason question comes from basic astronomy and climate concepts. Historically, Pluto was considered the outermost planet in our solar system and is extremely cold. You must judge whether the assertion about Pluto being the coldest planet is true and whether the given reason, involving slanting rays of the sun, is both correct and an accurate explanation. Understanding why distant bodies in the solar system are cold is crucial here.

Given Data / Assumptions:
- Assertion (A): Pluto is the coldest planet. - Reason (R): It receives slanting rays of the sun. - Pluto is very far from the sun compared to the inner planets. - The intensity of solar radiation decreases rapidly with distance from the sun.

Concept / Approach:
To answer, we need to recall that temperatures on planets are largely governed by how much solar energy they receive, which depends strongly on their distance from the sun. Rays are effectively parallel in space, and the idea of slanting rays is used mainly on Earth to explain temperature differences by latitude and time of day. For a distant object like Pluto, the key reason for low temperature is the very low overall intensity of sunlight, not slanting rays. We judge the truth of the assertion and then examine the reason separately.

Step-by-Step Solution:
Step 1: Evaluate Assertion (A). In many school level contexts, Pluto is treated as the outermost member of the planetary family and is extremely cold due to its great distance from the sun. Within that traditional framework, the assertion that Pluto is the coldest planet is taken as true. Step 2: Evaluate Reason (R). The statement says Pluto receives slanting rays of the sun. The term slanting rays usually refers to oblique sunlight at higher latitudes on Earth or at sunrise and sunset, not to the situation of a distant planet as a whole. The primary issue for Pluto is not slanting rays, but the tiny amount of solar energy per unit area that reaches it due to its large distance. Step 3: Even if one imagines the direction of sunlight relative to Pluto, the rays from the sun are essentially parallel and fall almost straight on the surface at some point. The low temperatures are due mainly to the inverse square law reduction in solar intensity with distance, not due to rays being slanting in any special sense. Step 4: Therefore, the reason is not accurate and should be considered false in the context of the explanation. We thus have a true assertion and a false reason.

Verification / Alternative check:
Consider another example on Earth. At the equator at noon, the sun is nearly overhead and its rays are almost vertical, which gives high intensity heating. At high latitudes, the sun is lower in the sky and rays are more slanting, so the same energy is spread over a larger surface area and the ground heats less. On Pluto and other distant bodies, the main factor is that the total energy arriving from the sun is extremely small because of the huge distance, not because the rays are especially slanted. This difference shows that applying the Earth based idea of slanting rays to Pluto's global coldness is incorrect.

Why Other Options Are Wrong:
- Saying both A and R are true would incorrectly accept the reason as a correct statement, which it is not. - Saying that both A and R are true and that R explains A is even more incorrect because R does not describe the main cause of Pluto's low temperature. - Saying that A is false but R is true does not match the educational context where Pluto is considered very cold due to distance. - Saying both A and R are false ignores the clear fact that Pluto is extremely cold, which is educationally emphasised as a true statement.

Common Pitfalls:
Students sometimes apply Earth specific climate explanations, such as slanting rays, to all planetary bodies without checking whether the mechanism really applies. Another pitfall is neglecting the impact of distance on solar intensity. This can lead to accepting any apparently familiar reason as correct. To avoid such errors, always identify the dominant physical factor responsible for the phenomenon described in the assertion.

Final Answer:
The assertion is true but the reason is false, so the correct choice is A is true but R is false.