Will wearing protective suit protect the baby in the last trimester from the x-ray radiation if the mum had to do chest xray?

I believe yes: You should call your obstetrician for the best answer, since i don't know why you had an x ray, or how many. But in general, yes, your baby should have been well protected from the harmful effects, which is precisely why they give you the protective suit.

Yes: The baby can be shielded effectively although it is not quite 100%. A chest x-ray is a very low exposure to begin with, comparable to flying from new york to la. This does not mean that it is ok to do without good reason. "routine" is not acceptable!