CORRECT!

By applying carburetor heat, the pilot introduces air into the carb that was warmed by the heat produced by the running engine. Carburetors are designed with a venturi which is used to suck fuel into the airstream heading to the cylinders. When the flow of a fluid (in this case, air) is restricted, the pressure and temperature of the fluid are both decreased. Depending on power settings and moisture content of the incoming air, the moisture can condense and freeze on the carburetor interior, eventually blocking the venturi and thus, the fuel flow. The application of carb heat helps to melt any accumulated carb ice and restore normal fuel flow.

But, the application of warm air to the carburetor reduces engine performance since warm air is less dense then cold air and doesn't support the same level of combustion as does colder air. This is why engine idle should always be checked with the carb heat ON during the pre-flight engine run-up. The introduction of the warmer air results in a reduction of engine RPM which could be enough of a reduction to cause the engine to quit altogether when the throttle is pulled out to idle during a landing approach, for example.