What happens to heating elements in a unit connected improperly to voltage?

When heating elements are connected improperly to voltage, they typically receive either too much or too little voltage. This can lead to excessive current flow which generates excessive heat. Over time, this overheating can cause physical damage to the heating elements, such as burning out the coils or destroying insulation. As a result, improper voltage connections can lead to failure of the heating elements, making this the correct answer.

In contrast, the idea that they operate more effectively does not hold because improper voltage does not lead to optimal functioning. Similarly, consuming less power is not accurate since an increase in voltage can lead to greater power consumption and damage. Lastly, the notion that they perform exactly as intended does not apply, as improper connections disrupt the normal operation and effectiveness of the heating elements.