The power spectral density (PSD) is a measure of the power distribution across different frequencies in a signal. In the case of white noise, the PSD is uniform throughout the frequency spectrum. This means that the power is evenly distributed across all frequencies.

White noise is a type of random signal that has a constant power density at all frequencies. It is called white noise because it contains equal power at all frequencies, just as white light contains equal power at all visible wavelengths.

To understand why the PSD of white noise is uniform throughout the frequency spectrum, let's break down the concept:

1. Definition of white noise:
- White noise is a random signal that has a constant power spectral density at all frequencies.
- It is characterized by its flat frequency response, meaning that it has equal energy at all frequencies.

2. Power Spectral Density (PSD):
- The PSD of a signal describes how the power of the signal is distributed across different frequencies.
- It is calculated by taking the Fourier transform of the autocorrelation function of the signal.
- The PSD provides information about the power or energy contained within specific frequency bands.

3. Uniform distribution of power:
- In the case of white noise, the power is evenly distributed across all frequencies.
- This means that the PSD of white noise is constant and uniform throughout the frequency spectrum.
- There are no specific frequency components that dominate or have more power than others.

4. Visual representation:
- When the PSD of white noise is plotted on a graph, it appears as a horizontal line at a constant value.
- This indicates that the power is the same across all frequencies.

In summary, the power spectral density of white noise is uniform throughout the frequency spectrum because it has equal power at all frequencies. This is why option C, "uniform," is the correct answer.