"I am going to mention that to the others."
Translation:Je vais mentionner cela aux autres.
I think "ça" should be accepted. From what I've read, what happens in practice is that "cela" is usually replaced by ça in spoken French. Since I want to be able to speak French as naturally as I can, I chose "ça" .
I also had "ca" not accepted, in favour of "cela".
In a previous sentence, Duo would not accept "cela" for 'that' and wanted 'ça'. What is the difference between 'cela' and 'ça'? I thought 'ça' was just a contraction for 'cela'?
Using "le" or "la" as an impersonal pronoun means "it", that's why "cela" is in the French sentence to mean "that".