In German problems olympiad 2014, the solution says that decomposition of arsine is not a redox reaction. Why would that be? Shouldn't H turn from -1 to 0 and As from 3+ to 0?

$$\ce{2AsH3 -> 2As + 3H2}$$

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    $\begingroup$ If they really said so, they probably implied that with electronegativity difference that small we may just as well consider both oxidation states 0 from the start, because they are arbitrary anyway. $\endgroup$ – Ivan Neretin Oct 5 '17 at 17:16

Often in chemistry "facts" depend on perspective. You're right that essentially H goes from -1 to 0 and As from 3+ to 0. But in general redox reaction involve two different chemical species. In this case it is better to think of the reaction as a decomposition reaction rather than a redox reaction.

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  • $\begingroup$ Decomposition reactions are autoredox reaction (Disproportionation ).Are they not ? $\endgroup$ – Winston Cahya Oct 21 '17 at 5:48

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