Four particles each of mass $m$ are placed at the vertices of a square of side $l.$ The potential energy of the system is

• A
  $ - \frac{{\sqrt 2 G{m^2}}}{l}\left( {2 - \frac{1}{{\sqrt 2 }}} \right)$
• B
  $ - \frac{{2G{m^2}}}{l}\left( {2 + \frac{1}{{\sqrt 2 }}} \right)$
• C
  $ - \frac{{4G{m^2}}}{l} - \frac{{2G{m^2}}}{{\sqrt 2 l}} = - \frac{{2G{m^2}}}{l} (2 + \frac{1}{\sqrt{2}})$
• D
  $ - \frac{{2G{m^2}}}{l}\left( {\sqrt 2 - \frac{1}{{\sqrt 2 }}} \right)$