Incorrect!

When should you use your vehicle's horn?

To alert others to your presence
Correct answer
To allow you right of way
You selected this answer
To greet other road users
To signal your annoyance

DVSA theory test explanation

You must not use your vehicle's horn between 11:30pm and 7am in a built-up area or when you're stationary, unless a moving vehicle poses a danger. Its function is to alert other road users to your presence.