Which of these is not a compound noun? Options : Traffic lights Traffic police Traffic stop Traffic system

The option that is not a compound noun is "Traffic stop".

A compound noun is a noun that is made up of two or more words. Each word contributes to the overall meaning of the noun.

In the options given, "Traffic lights", "Traffic police", and "Traffic system" are all compound nouns because they are made up of two words that work together to create a new meaning.

However, "Traffic stop" is not a compound noun. While it is made up of two words, these words do not work together to create a new meaning. Instead, "stop" is a verb that describes an action being taken in relation to the traffic. Therefore, "Traffic stop" is not a compound noun.