Which is or Which are?

Question

Could you please check if the following sentence is grammatically correct:

"There are a number of reasons for this trend, which is having a significant impact on both family life and on the community as a whole."

I think it should be "which are" instead of "which is" as I think "which" modifies "a number of reasons", which is a plural noun phrase.

Thank you!

Answer 1

As you're referring to the trend, then it's singular, is.

Had you been referring to the number of reasons, then it would have been plural, are.

The trend is having an impact, the number of reasons isn't.