(1) ① When +5-valent arsenic and vitamin C are eaten together, toxic +3-valent arsenic will be generated, and the valence state of Sn will change from +5 to +3, so+5-valent arsenic is oxidized as an oxidant, so the answer is: oxidation;

(2) +5-valent arsenic is oxidizing and can oxidize reducing substances, and +5-valent arsenic reacts with vitamin C to generate +3-valent arsenic, which shows that vitamin C acts as a reducing agent and reflects reducibility, so the answer is: reduction; Reduction;

(2) In this reaction, only the electron loss valence of Al element increases, and the valence state of Al element changes from 0 to +3, so the amount of substances that completely react with 10mol is 30mol, and the number of transferred electrons is 30NA；; In this reaction, the valence of Al element changed from 0 to +3, and that of N element changed from +5 to 0. According to the equation, the number of electrons transferred by the reaction is 30, and the direction and number of electrons transferred by the double-line bridge are,

So, the answer is: 30NA；; .