explain in detail how to find valency of barium…
To find out the valency of any element just write the electronic configuration and see how the element can attain the inert gas configuration. For example lets take Barium(Z= 56)
Ba = [Xe] 6s2 or 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p66s2
So, if barium looses the 2 electrons it will attain Xe like configuration. So, its valency is two.
Similarly, find for other elements.