Which of the following statements are incorrect?

Options

A. Wave pulses in strings are transverse waves.
B. Sound waves in air are transverse waves of compression and rarefaction.
C. The speed of sound in air at `20^@C` is twice that at `5^@C`.
D. A 60dB sound has twice the intensity of a 30 dB sound.

Explanation

To determine which statements are incorrect, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement A: "The wave pulse in a string are transverse waves."**
- **Analysis:** This statement is true. In a string, the wave pulses are indeed transverse waves, where the particles of the medium move perpendicular to the direction of wave propagation.

2. **Statement B: "Sound waves in air are transverse waves of compression and rarefaction."**
- **Analysis:** This statement is incorrect. Sound waves in air are longitudinal waves, not transverse. In longitudinal waves, the particles of the medium oscillate parallel to the direction of wave propagation, creating regions of compression and rarefaction.

3. **Statement C: "The speed of sound in air at 20 degrees Celsius is twice that of 5 degrees Celsius."**
- **Analysis:** This statement is also incorrect. The speed of sound in air is proportional to the square root of the absolute temperature (in Kelvin). The temperatures in Kelvin are 293 K (20°C) and 278 K (5°C). The ratio of the speeds is not 2, as the temperature must be quadrupled to double the speed of sound.

4. **Statement D: "A 60 decibel sound has twice the intensity as that of a 30 decibel sound."**
- **Analysis:** This statement is incorrect. The relationship between intensity and decibels is logarithmic. A difference of 10 decibels corresponds to a tenfold increase in intensity. Therefore, a sound that is 60 dB is not twice but rather significantly more intense than a sound at 30 dB.

### Conclusion:
The incorrect statements are B, C, and D.

### Final Answer:
- **Incorrect Statements:** B, C, D