Question

if barium ions have a charge of 2= nd hydroxide ions have a charge of 1-, the compound calcium is what?

Answer 1

what dose porosity mean?

Answer 2

First, if you have a question, it is much better to put it in as a separate post in <Post a New Question> rather than attaching it to a previous question, where it is more likely to be overlooked.

Since this is not my area of expertise, I searched Google under the key words "<I>porosity</I>" to get these possible sources:

http://www.google.com/search?client=safari&rls=en&q=porosity&ie=UTF-8&oe=UTF-8

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.