A: The earth's magnetic field not only varies from point to point in space, it also changes with time
R: The earth's core is known to contain iron yet geologists do not regard this as a source of the earth's magnetism.

Options

A. If both Assertion & Reason are the true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reson is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To analyze the statements provided in the question, we will break down the assertion (A) and the reason (R) step by step.

### Step 1: Analyze the Assertion (A)
The assertion states that "The earth's magnetic field not only varies from point to point in space, it also changes with time."

- **Explanation**: This statement is correct. The Earth's magnetic field does indeed vary in strength and direction at different locations on the surface of the Earth. Additionally, it is known to change over time due to various geological and solar activities, including phenomena such as geomagnetic reversals.

### Step 2: Analyze the Reason (R)
The reason states that "The earth's core is known to contain iron yet geologists do not regard this as a source of the earth's magnetism."

- **Explanation**: This statement is also correct. While the Earth's core does contain iron, it is primarily in a molten state. Molten iron does not exhibit ferromagnetic properties, which are necessary for the generation of a magnetic field. Therefore, geologists do not consider the molten iron in the Earth's core to be a source of the Earth's magnetism.

### Step 3: Determine the Relationship Between A and R
Now we need to determine if the reason (R) correctly explains the assertion (A).

- **Explanation**: Although both statements are correct, the reason does not provide a direct explanation for the assertion. The assertion discusses the variability of the Earth's magnetic field over space and time, while the reason addresses the composition of the Earth's core and its magnetic properties. Thus, while both statements are accurate, the reason does not explain why the Earth's magnetic field changes over time.

### Conclusion
Based on the analysis:
- Both the assertion (A) and the reason (R) are correct.
- However, the reason (R) does not correctly explain the assertion (A).

Thus, the answer is option 2: Assertion is correct, Reason is correct, but Reason is not the correct explanation for Assertion.

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