State the $Hardy-Schulze$ rule.

• A
  Coagulation power of non-electrolytes is better than electrolytes.
• B
  The ions carrying charge opposite to that of the sol particles are effective in causing coagulation,and the greater the valence of the coagulating ion,the greater is its power to cause coagulation.
• C
  The charge of the ions has no effect on the coagulation of the sol.
• D
  Coagulation of the sol occurs only by ions that have the same charge as the sol.