Statement I: The apparent freqeuncy which is the frequency as noted by an observer or an observing detection device of the acoustic wave that moves from the source to the observer propagating in a medium may be different from its true frequency.
Statement II: A source in motion relative to an observer sends out less or more number of waves per metre distance in the medium and an observer in motion collects less or more number of waves per second that when both of them remain at rest relatively.

Options

A. (a)Statement I is true, Statement II is true: Statement II is a correct explanation for statement I.
B. (b)Statement I is true, Statement II is true, Statement II is NOT a correct explanation for Statement I.
C. (c)Statement I is true, Statement II is false
D. (d)Statement I is false: Statement II is true

Explanation

To analyze the given statements regarding the apparent frequency of sound waves and the effects of motion, we can break down the solution step by step.

### Step 1: Understand Statement I
**Statement I:** The apparent frequency, which is the frequency noted by an observer of an acoustic wave, may differ from its true frequency when the source or observer is in motion.

**Explanation:** This statement is based on the Doppler Effect, which describes how the frequency of a wave changes for an observer moving relative to the source of the wave. When the source of sound moves towards the observer, the waves are compressed, leading to a higher apparent frequency. Conversely, if the source moves away, the waves are stretched, resulting in a lower apparent frequency.

### Step 2: Analyze Statement II
**Statement II:** A source in motion relative to an observer sends out fewer or more waves per meter distance in the medium, and an observer in motion collects fewer or more waves per second compared to when both are at rest.

**Explanation:** This statement also relates to the Doppler Effect. When the source moves, the rate at which waves are emitted changes due to the motion. If the source moves towards the observer, the observer encounters more waves per second (higher frequency). If the observer moves towards the source, they also encounter more waves per second. Thus, both the motion of the source and the observer affects the frequency perceived.

### Step 3: Conclusion
Both statements are true. However, Statement II does not provide a correct explanation for Statement I. While both statements discuss the effects of motion on frequency, Statement II elaborates on the mechanics of wave interaction, which is not a direct explanation of why the apparent frequency differs from the true frequency.

### Final Answer
- Statement I is true.
- Statement II is true but does not correctly explain Statement I.
- Therefore, the correct option is **B**.

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