John has three jars.
He decided to sell them.
Or
He decided to sell that.
What is the difference between these two sentences?
He decided to sell them.
PRONOUN
1 [third person plural] Used as the object of a verb or preposition to refer to two or more people or things previously mentioned or easily identified. ‘I bathed the kids and read them stories’
You would use it for a singular item in the same structure.