(1) acetic acid is composed of three elements: carbon, hydrogen and oxygen; the mass ratio of carbon to oxygen in acetic acid is (12×2): (16×2) = 3:4; one molecule of acetic acid contains four atoms of hydrogen; sodium chloride is formed by combining anion and cation, and the cation is a sodium ion with the ion symbol Na+.

(2) by the atomic structure of the element can be seen: the number in the circle is 17, the element's atomic nuclear charge of 17; the atom's outermost electron layer has 7 electrons, in the chemical reaction is easy to get 1 electron and the formation of cations.

The answers are: (1) 3; 3:4; 4; Na+; (2) 17; 1.