Section 19. The city council at any time may request from the mayor, or, under Plan D or E, from the city manager, specific information on any municipal matter within its jurisdiction, and may request him to be present to answer written questions relating thereto at a meeting to be held not earlier than one week from the date of the receipt by the mayor, or, under Plan D or E, by the city manager, of said questions. The mayor, or, under Plan D or E, the city manager, shall personally, or through the head of a department or a member of a board, attend such meeting and publicly answer all such questions. The person so attending shall not be obliged to answer questions relating to any other matter. The mayor, or, under Plan D or E, the city manager, may attend and address the city council in person or through the head of a department, or a member of a board, upon any subject.