The type of reaction in above reaction is refered to as a disproportionation reaction .It sometimes used to describe desymmetrizing reaction.in the equation above compounds of intermediate oxidation state are converted to two different compound, that is Clo3 ions and 2cl-
You did not include the statements but since magnesium chloride is ionic substance that we know that magnesium and chlorine formed an ionic bond. Therefore your statement most likely will talk about how one magnesium atom gave up 2 electrons while two chlorine atoms took 1 electron. The reaction looks like Mg+2Cl⇒MgCl₂.
I hope this helps. Let me know in the comments if anything is unclear.
B. I’m sorry if I’m wrong ! Wasn’t sure about this question .