Whenever any petition, as provided in section 19-501, shall be filed with the city clerk and shall contain the required number of signatures of qualified electors, asking for the submission of additional or alternative articles or sections in the complete form in which such articles or sections are to read as amended, such articles or sections shall be deemed to be proposed for adoption by the qualified electors of the city with the same force and effect as if proposed by the charter convention, and the article or section which receives the majority of all the votes cast for and against such additional or alternative articles or sections shall be declared adopted, and certified to the Secretary of State, a copy deposited in the archives of the city, and shall become the charter or part thereof, of such city.