Which of the following are incorrect ?

Options

A. Presence of moisture in air decreases density of air.
B. Sound heard in `CO_(2)` is more intense than that heard in air.
C. Mechanical waves transfer energy and matter from one point to another.
D. The distance between a node and and adjoining antinode in a stationary wave is `(lambda)/(2)`.

Answer

To solve the question of identifying the incorrect statements among the given options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: The presence of moisture in the air decreases the density of the air.**
- **Analysis:** The air is primarily composed of nitrogen (N2) and oxygen (O2). The molar mass of nitrogen is approximately 28 g/mol, and oxygen is about 32 g/mol. Water (H2O) has a molar mass of 18 g/mol. When moisture is added to the air, the water vapor replaces some of the heavier nitrogen or oxygen molecules. Since H2O is lighter than both N2 and O2, the overall mass of the air decreases, leading to a decrease in density.
- **Conclusion:** This statement is **true**.

2. **Statement 2: Sound heard in CO2 is far more intense than that heard in Air.**
- **Analysis:** The intensity of sound in a medium is directly proportional to the density of that medium. The molar mass of CO2 is 44 g/mol, which is heavier than the average molar mass of air (approximately 29 g/mol). Therefore, the density of CO2 is greater than that of air. Since intensity increases with density, sound will be more intense in CO2 than in air.
- **Conclusion:** This statement is **true**.

3. **Statement 3: Mechanical waves transfer energy and matter from one point to another.**
- **Analysis:** Mechanical waves, such as sound waves, transfer energy through the oscillation of particles in the medium, but they do not transfer matter. The particles oscillate around their equilibrium positions, and while energy is transmitted through the wave, the matter itself remains in place.
- **Conclusion:** This statement is **false** (incorrect).

4. **Statement 4: The distance between a node and the adjoining antinode in a stationary wave is λ/2.**
- **Analysis:** In a stationary wave, the distance between a node (point of zero amplitude) and the nearest antinode (point of maximum amplitude) is actually λ/4, not λ/2. The full wavelength (λ) is the distance between two consecutive nodes or two consecutive antinodes.
- **Conclusion:** This statement is **false** (incorrect).

### Final Conclusion:
The incorrect statements are:
- **Statement 3:** Mechanical waves transfer energy and matter from one point to another.
- **Statement 4:** The distance between a node and the adjoining antinode in a stationary wave is λ/2.