The answer options are testing your knowledge on the behavior of sound velocity in different conditions.

Option 1 states that the velocity of sound in air increases with the increase of temperature. This is correct because as the temperature rises, the molecules in the air move faster, increasing the speed of sound.

Option 2 states that the velocity of sound in air is independent of pressure. This is true assuming that the temperature remains constant. Under such conditions, variations in pressure would not affect the speed of sound.

Option 3 claims that the velocity of sound in air decreases as the humidity increases. This is the incorrect statement. In actuality, as humidity increases, or the amount of water vapor in the air increases, the speed of sound also increases.

Finally, option 4 asserts that the velocity of sound in air is not affected by the individual changes in amplitude and frequency. This is also true, as the speed of sound is not determined by these factors.

Hence, regarding the question, option 3 is the incorrect statement as the velocity of sound increases with humidity, not decreases.