(A) : If an electron is not deflected while passing through a certain region of space, then only possibility is that there is no magnetic field in this region.
(R) : Magnetic force on a charged particle is directly proportional to specific charge of particle.

Options

A. Both 'A' and 'R' are true and 'R' is the correct explanation of 'A'.
B. Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
C. 'A' is true and 'R' is false
D. 'A' is false and 'R' is false

Answer

To solve the question, we will analyze both the assertion and the reason provided, and determine their validity.

### Step 1: Analyze the Assertion
The assertion states: "If an electron is not deflected while passing through a certain region of space, then the only possibility is that there is no magnetic field in this region."

- When an electron moves through a magnetic field, it experiences a magnetic force given by the formula:
\[ F = q(\mathbf{v} \times \mathbf{B}) \]
where \( F \) is the magnetic force, \( q \) is the charge of the electron, \( \mathbf{v} \) is its velocity, and \( \mathbf{B} \) is the magnetic field.
- The electron will not be deflected if the magnetic force acting on it is zero. This can happen in two scenarios:
1. There is no magnetic field (\( \mathbf{B} = 0 \)).
2. The angle \( \theta \) between the velocity vector \( \mathbf{v} \) and the magnetic field vector \( \mathbf{B} \) is 0 degrees (parallel) or 180 degrees (anti-parallel), which results in \( \sin \theta = 0 \).

Thus, the assertion is **false** because it does not account for the scenario where the electron is moving parallel to the magnetic field.

### Step 2: Analyze the Reason
The reason states: "Magnetic force on a charged particle is directly proportional to the specific charge of the particle."

- The magnetic force \( F \) is given by:
\[ F = qvB \sin \theta \]
- The specific charge is defined as the charge per unit mass of the particle. However, the magnetic force depends on the charge \( q \) and not directly on the specific charge. The relationship does not imply direct proportionality to specific charge, as it is also influenced by velocity and magnetic field strength.

Thus, the reason is **true** in terms of the relationship of force to charge, but it does not accurately reflect the concept of specific charge in the context of the assertion.

### Conclusion
- Assertion (A) is **false**.
- Reason (R) is **true**.

### Final Answer
The correct option is that the assertion is false and the reason is true.

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