Can I use "it" instead of "them" to mean a whole unit for plural nouns in spoken language?
A: These flowers are so pretty.
B: Let me put it in a vase.

A: Here are 20 sets of document I photocopied.
B: Thanks. I will bring it to the meeting room.

A: I bought a lot of vegetables from the market.
B: I'm going to chop it all.

So, are they interchangeable?

Thank you.

Question

Can I use "it" instead of "them" to mean a whole unit for plural nouns in spoken language?
A: These flowers are so pretty. 
B: Let me put it in a vase.

A: Here are 20 sets of document I photocopied.
B: Thanks. I will bring it to the meeting room.

A: I bought a lot of vegetables from the market.
B: I'm going to chop it all.

So, are they interchangeable?

Thank you.

Answer

No, you need to use "them" in all the examples you provide.
Hope this helps!

Answer

Yes, I say it that way too. Here is an explanation I found online. 
"Uncountable nouns are for the things that we cannot count with numbers. Uncountable nouns are used with a singular verb."