How can you identify a redox reaction? A. Electrons have transferred from one atom to another.
B. The number of protons has changed in an atom.
C. The charges on each side of the equation cancel.
D. Metal atoms have rearranged in the compounds.

I’m not sure about this question

Elements would be the right answer

Electron equations of the given changes are as follow,a)                              cu      →      cu⁺²  + 2e⁻b)                              mg⁺²  +  2 e⁻      →      mgc)                              cl⁻    →      cl  +  1e⁻d)                              s  +  2 e⁻    →      s²⁻e)                                o²⁻      →      o  +  2 e⁻f)                              p  +  3 e⁻    →      p³⁻g)                              fe²⁺    →      fe³⁺  + 1 e⁻h)                              s²⁻    →      s⁴⁺  +  6 e⁻

I'd say your answer would be the sides of a metal pan become hot when the pan is placed on the stove burner