Out of the options given below, choose the sentence which is grammatically incorrect: 

 The number of cars on the road have increased significantly.

The correct answer is Option (1) - The number of cars on the road have increased significantly.

The subject "The number" is singular, so the verb should be "has" instead of "have." The correct sentence is: The number of cars on the road has increased significantly.

OTHER OPTIONS

• "We have a meeting tonight.": This is grammatically correct and clear.
• "Have you made the necessary changes?": This is grammatically correct and clear.
• "This is outrageous.": This is grammatically correct and clear.