posted by sam .
why have he brackets around the (OH)2
and not just OH2
it ask to lsit each element and the number of atoms present.
If it was just OH2 then it would be a differnt element, water actually. The brackets are there to indicate that it is together, and to show you there is 2 of each, the 2 just at the end as you put it would indicate only 1 oxygen atom and 2 hydrogen atoms. Because it is a compound it is placed together in brackets.
See my response to Sarah's original question.
I should have said to look at Sam's original post and my response.