What is the oxidation state of carbon in $CaC_{2}$ and $K_{2}C_{2}O_{4}$ respectively?
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Logic Tip: The $C_2^{2-}$ ion in calcium carbide is the acetylide ion, featuring a carbon-carbon triple bond ($[:C \equiv C:]^{2-}$). Since the two identical carbon atoms equally share the $-2$ charge, each carbon naturally carries a formal oxidation state of $-1$.