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2. http://en.wikipedia.org/wiki/Alkali_metal
, Accessed 3 Mar 2015
3. http://www.studyvilla.com/Images/periodictable4.jpg
, Accessed 25 Feb 2014
4. http://tabish.freeshell.org/physics/Sr/
, Accessed 25 Feb 2014
5. http://tabish.freeshell.org/physics/Sr/gas-aggr.gif
, Accessed 25 Feb 2014