(A): Mechanical waves cannot be polarised.
(R): Electromagnetic waves cannot be polarised.

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. Both 'A' and 'R' are false

Answer

To analyze the statements given in the question, we need to evaluate both the assertion (A) and the reason (R) separately.

**Step 1: Evaluate the Assertion (A) - "Mechanical waves cannot be polarised."**

Mechanical waves can be classified into two types: transverse waves and longitudinal waves.

- **Transverse Waves:** In transverse waves, the oscillations occur perpendicular to the direction of wave propagation. These waves can be polarized. An example of a transverse mechanical wave is a wave on a string.

- **Longitudinal Waves:** In longitudinal waves, the oscillations occur parallel to the direction of wave propagation. These waves cannot be polarized. An example of a longitudinal mechanical wave is a sound wave.

Since only longitudinal mechanical waves cannot be polarized, the assertion that "Mechanical waves cannot be polarised" is incorrect. Therefore, the assertion (A) is false.

**Step 2: Evaluate the Reason (R) - "Electromagnetic waves cannot be polarised."**

Electromagnetic waves are inherently transverse waves.

- Since electromagnetic waves are transverse in nature, they can indeed be polarized. Polarization of electromagnetic waves occurs when the electric field vector of the wave oscillates in a particular direction.

Thus, the reason (R) stating that "Electromagnetic waves cannot be polarised" is also false.

**Step 3: Conclusion**

Both the assertion (A) and the reason (R) are false. Therefore, the correct answer is that both statements are incorrect.

### Final Answer:
Both the assertion (A) and reason (R) are false.

---