The tea was no longer hot or (brewed) so the 5th didn’t dissolve like the others because the tea was hot or warm enough anymore it cooled down. So the sugar won’t dissolve no more.
Moles = weight in grams / molecular weight.
So I would divide the "grams of barium" by its molecular weight (which is 137.3) to get "moles of barium". :)
Answer:
This 2.5061243 moles is in 4 liters.
