Which of the following would  notincrease the velocity of a sound wave in air?  

Simple. We know the relation v=fλv=fλ, where vv is velocity, ff is frequency and λλis wavelength.

For velocity to be constant, we get the relation f∝1λf∝1λ. This means that you can increase or decrease the frequency, and the wavelength will change appropriately so that the velocity remains constant.

Thus, only frequency/wavelength changes will not change the velocity of a wave.

f is prop to m1xm2 double m1 double force