Assertion: To protect any instrument from external magnetic field, it is put inside an iron body.
Reason: Iron is a magnetic substance.

Options

A. If both Assertain and Reason are true and Reason is the correct explanation of Assertain
B. If both Assertain and Reason are true but Reason is not correct explantion of Assertain
C. If Assertion is true but Reason is false
D. If Assertion is false but Reason in true.

Explanation

To solve the assertion and reason question, we will analyze both the assertion and the reason step by step.

### Step 1: Understand the Assertion
The assertion states that to protect any instrument from an external magnetic field, it should be placed inside an iron body. This implies that iron can shield or block the magnetic field from affecting the instrument.

**Hint:** Consider how materials interact with magnetic fields and what properties they possess.

### Step 2: Analyze the Properties of Iron
Iron is classified as a ferromagnetic material. This means it has a high magnetic susceptibility, which allows it to become magnetized in the presence of an external magnetic field. When placed in an external magnetic field, iron tends to concentrate the magnetic field lines within itself.

**Hint:** Recall the definition of ferromagnetic materials and their behavior in magnetic fields.

### Step 3: Understand the Effect of Iron on Magnetic Fields
When an external magnetic field is applied, the iron body will attract the magnetic field lines. As a result, the magnetic field strength inside the iron body is different from the external field. The iron effectively redirects the magnetic field lines, allowing the space inside the iron body to have a reduced magnetic field or even a negligible effect from the external field.

**Hint:** Think about how magnetic field lines behave when they encounter different materials.

### Step 4: Analyze the Reason
The reason given is that iron is a magnetic substance. This is true, as iron's ferromagnetic properties allow it to interact with magnetic fields significantly. Therefore, the reason supports the assertion.

**Hint:** Consider how the properties of iron directly relate to its ability to shield against magnetic fields.

### Step 5: Conclusion
Both the assertion and the reason are true. The assertion is correct because placing an instrument inside an iron body does protect it from external magnetic fields. The reason is also true because iron is indeed a magnetic substance, and its properties explain why it can provide such protection. Therefore, the correct conclusion is that both the assertion and reason are true, and the reason is a correct explanation for the assertion.

**Final Answer:** Both the assertion and reason are true, and the reason is a correct explanation for the assertion.