A person desiring to intervene shall serve a motion to intervene upon the parties as provided in Rule 5. The motion shall state the grounds therefor and shall be accompanied by a pleading setting forth the claim or defense for which intervention is sought. The same procedure shall be followed when a statute gives a right to intervene. When the constitutionality of an act of the General Assembly affecting the public interest is drawn into question in any action, the movant shall serve a copy of the pleading, motion or other paper first raising the challenge upon the Attorney General.