In a gas, such as air, an increase in temperature results in a(n) in the speed of sound.

So we want to know what happens with the speed of sound in air when the temperature of the air increases. Since molecules with higher temperature have more kinetic energy, because kinetic energy is directly proportional with temperature, they can vibrate faster. So the speed of sound increases with the increase of temperature. 

The answer is b.the gaseous state is electrically positive, while the plasma state is electrically negative.