Why should you replace a scratched helmet visor?

You answered correctly. A scratched helmet visor should be replaced because scratches can restrict your vision and increase glare from headlights or sunlight. Both factors can make it harder to see clearly while riding, especially in low light or at night. However, scratches do not make the visor more likely to mist up, so that option is not correct. It's important to keep your visor clear and in good condition for safety. If it becomes scratched, replacing it will help you maintain the best possible visibility on the road.