The **front fog lights** are optional on a vehicle in case of fog. These lights help improve visibility in adverse conditions such as fog, snow, heavy rain, and smoke. They can be used together with the position lights, as well as with the high and low beam lights. This means you can choose to turn them on to improve your visibility without it being mandatory.

On the other hand, the **rear fog lights** are more restricted in use and should only be turned on in situations of great need, when visibility conditions are extremely poor. This makes them mandatory in certain circumstances, unlike the front fog lights.

Finally, the **brake lights** are not optional nor are they related to fog, as their function is to indicate to other drivers that the vehicle is slowing down or stopping.