Which of the following statements is incorrect?

• A
  The amount of substance of a system which contains as many elementary entities as there are atoms in $0.012 \ kg$ of carbon-$12$ is known as one mole.
• B
  According to Avogadro's law,equal volumes of gases at the same temperature and same pressure should contain equal number of molecules.
• C
  According to Dalton's atomic theory,chemical reactions involve the reorganization of atoms. These are neither created nor destroyed in a chemical reaction.
• D
  The mass of one mole of a substance in milligrams is called its molar mass.