¹[(1) Any director elected under clause (d) of section 10 may, by giving notice in writing to the Chairman of the Board, resign from his office and on such resignation being accepted, shall be deemed to have vacated his office.]
     (2) A casual vacancy in the office of an elected director shall be filled by election and a director so elected shall hold office for the unexpired portion of the term of his predecessor.
     (3) No act or proceeding of the Board shall be questioned on the ground merely of the existence of any vacancy in, or any defect in the constitution of the Board.