(A) : The sky waves are not used in the transmission of television signals.
(R) : Sky waves are mechanical waves.

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 abd 'R' false
D. A' is false and 'R' is false

Answer

To solve the question, we need to analyze the statements (A) and (R) provided:

**Statement (A):** The sky waves are not used in the transmission of television signals.
**Statement (R):** Sky waves are mechanical waves.

### Step-by-Step Solution:

1. **Understanding Sky Waves:**
- Sky waves are radio waves that are reflected back to Earth by the ionosphere. They are primarily used for long-distance communication, especially in the HF (High Frequency) band.

2. **Transmission of Television Signals:**
- Television signals are typically transmitted in the VHF (Very High Frequency) and UHF (Ultra High Frequency) bands, which range from 30 MHz to 300 MHz and 300 MHz to 3 GHz, respectively.
- The ionosphere, which reflects sky waves, is effective for frequencies below 30 MHz. Therefore, sky waves are not suitable for the transmission of television signals that operate at higher frequencies.

3. **Evaluating Statement (A):**
- Since television signals operate at frequencies higher than what sky waves can effectively transmit (due to the limitations of the ionosphere), statement (A) is true.

4. **Understanding Mechanical Waves:**
- Mechanical waves require a medium (like air, water, or solid substances) to propagate. Sky waves, being radio waves, are electromagnetic waves, which do not require a medium to travel.
- Therefore, statement (R) is incorrect because sky waves are not mechanical waves; they are electromagnetic waves.

5. **Conclusion:**
- Since statement (A) is true and statement (R) is false, we conclude that:
- (A) is true.
- (R) is false.

### Final Answer:
- **(A) is true, (R) is false.**