Four different whistles, when blown, emit pure notes with the frequencies, 0.2 kHz, 10 kz, 25 kHz, 200 kHz. How many of the frequencies are above the normal audible range for humans?

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To determine how many of the given frequencies are above the normal audible range for humans, we need to follow these steps:

### Step 1: Understand the Normal Audible Range
The normal audible range for humans is typically from 20 Hz (0.02 kHz) to 20 kHz (20,000 Hz). Frequencies below 20 Hz are considered infrasound, and frequencies above 20 kHz are considered ultrasound.

### Step 2: List the Given Frequencies
The frequencies provided in the question are:
- 0.2 kHz
- 10 kHz
- 25 kHz
- 200 kHz

### Step 3: Compare Each Frequency to the Audible Range
Now, we will compare each frequency to the audible range:
- **0.2 kHz**: This is 200 Hz, which is within the audible range.
- **10 kHz**: This is 10,000 Hz, which is also within the audible range.
- **25 kHz**: This is 25,000 Hz, which is above the audible range.
- **200 kHz**: This is 200,000 Hz, which is also above the audible range.

### Step 4: Count the Frequencies Above the Audible Range
From our comparison:
- Frequencies above the audible range: 25 kHz and 200 kHz.
- Total count of frequencies above the audible range: 2.

### Final Answer
Thus, **2 frequencies** are above the normal audible range for humans.

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