What does it refer to?

I think "it" refers to substance B [:^)]

Thanks UsamaH,

Can you please provide me with an explanation?

JM

It's impossible to say whether the writer meant that A will do something or B will do something. Perhaps it means the A/B mixture.

I considered "B" as I thought of it like that:

Substance "B" was firstly alone and is not allowed to do something, but when substance "A" was added, It allowed it (B) to do that thing.

Despite of my explanation, I would rather prefer GrammarGeek's explanation instead.

Thanks for stopping by, GG

... How did you know that WAS the answer I was searching for?

Thanks again!

JM

Thanks UH for coming through once more

I got your point. Likewise, I like GG's explanation. No matter how grammatically correct it may be, it does not make any sense if we the readers are left confused.

Thanks again.

You are welcome.

jazzmasterNo matter how grammatically correct it may be, it does not make any sense if we the readers are left confused.

jazzmaster, that is the #1, most important rule of ANY writing - make it clear and easy for the reader to know what you meant!

It is more important than any rule of grammar, or any style guide.

Let's say it again!

GG, thanks for the overwhelming praise. I am flattered. Come to think of it, I did say it in pretty concise, short and sweet way, did I not?

Sadly, there are so many ESL teachers who are so grammatically narrow minded that they tend to forget the most important rule of all: "Unless readers understand what you are saying loud and clear in one shot, that sentence does not mean $#@*."

deleted : accidental double posting