Test and analysis: ① TiO 2+2cl2+2ticl4+2co2ticl4+2mg2 MgCl2+Ti.

The valence change of chlorine and carbon in chemical formula 1; The valence change of titanium and magnesium in chemical formula 2; So choose D.

Note: General reaction formulas of four basic reaction types:

1. chemical reaction: A+B=AB

2. Decomposition reaction: AB = A+B.

3.3. Displacement reaction: A+BC=B+AC

4. Double decomposition reaction: AB+CD=AD+CB.

The oxidant gains electrons, the valence is reduced, and the oxidation is strong; Oxidation products have weak oxidation; Therefore, we can judge the oxidation strength of substances.

Reducing agent loses electrons and its valence state increases, so it has strong reducibility. The reduction product has weak reducibility; Therefore, the reducibility of substances can be judged.