Introduction:
When an observer moves towards a stationary source of sound, the apparent frequency of the sound changes due to the relative motion between the source and observer. This change in frequency is known as the Doppler effect. The Doppler effect can be observed for both sound and light waves.

Explanation:
To understand the apparent increase in frequency when an observer moves towards a stationary source of sound, let's consider the following scenario:

Scenario:
An observer is moving towards a stationary source of sound with a velocity one-tenth the velocity of sound.

Key formula:
The formula for the apparent frequency (f') observed by the moving observer is given by:

f' = (v + vo) / (v + vs) * f

Where:
f' = Apparent frequency observed by the moving observer
f = Actual frequency of the source
v = Velocity of sound in the medium
vo = Velocity of the observer
vs = Velocity of the source

Explanation of the formula:
The formula accounts for the change in frequency due to the relative motion between the source, observer, and the medium. The numerator (v + vo) represents the relative velocity of the observer towards the source, and the denominator (v + vs) represents the relative velocity of the source towards the observer.

Calculation:
In the given scenario, the observer is moving towards the source with a velocity one-tenth the velocity of sound. Let's assume the velocity of sound (v) is denoted as 10v (for simplicity).

Substituting the values in the formula:

f' = (10v + 0.1v) / (10v + 0) * f
= 10.1v / 10v * f
= 1.01 * f

Therefore, the apparent frequency (f') observed by the moving observer is 1.01 times the actual frequency (f) of the source.

Conclusion:
The apparent increase in frequency is 1.01 times the actual frequency, which is equivalent to a percentage increase of 1.01 - 1 = 0.01 or 0.1%. Hence, the correct answer is option 'C' - 10%.