(1) 1 norfloxacin contains 16 carbon atoms and 18 hydrogen atoms, so the ratio of carbon and hydrogen atoms in norfloxacin molecule is 16: 18 = 8: 9.

(2) The mass fraction of nitrogen in norfloxacin is14× 3319×100% ≈13.2%.

(3) According to the meaning of the question, taking norfloxacin 400mg each time, 400mg=0.4g, each 0. 1g, the number of norfloxacin tablets each time is 0.4g÷0. 1g=4; Take it twice a day, so the number of times to take norfloxacin a day is 4 × 2 = 8; 10 day is a course of treatment, and the frequency of taking norfloxacin in a course of treatment is 8 × 10=80. The mass of 80 norfloxacin tablets is 0. 1g×80=8g, in which the mass of fluorine-containing element is 8g × 19 3 19× 65438.

So the answer is: (1) 8: 9; (2) 13.2%; (3)476.5 mg.