When a cold front passes your loction, the temperature falls as a result air density increases, decreases or stays the same

 When a gas is cooled, it contracts. In a sealed environment, the pressure would therefore reduce, as the molecules try to get closer together, that is, push outwards less. But in the atmosphere, the closer-packed molecules (or atoms, of course) make the air more dense, therefore heavier.

If you were at a higher elevation, the cooling is caused by the reduced pressure causing the molecules to move further apart. The temperature reduces about 1 degree Centigrade for every 100metres gain in elevation.

Any good?

A., d., and f i think

Sound energy is produced when an object vibrates. examples are 1- a balloon popping2-a whistle3- a waterfall