Answer:
The oxidizing agent is chlorine.
Explanation:
Oxidation-reduction reactions or redox reactions are those in which an electron transfer occurs between the reagents. An electron transfer implies that there is a change in the number of oxidation between the reagents and the products.
The species that supplies electrons is the reducing agent (that is, it is that species that oxidizes, yielding electrons and increasing its positive charge, or decreasing the negative one causing the reduction of the other species) and the one that gains them is the oxidizing agent (that is, it is that species that is reduced, capturing electrons and increasing its negative charge, or decreasing its positive charge, causing oxidation of the other species).
Between a reaction between chlorine and calcium, calcium acts as a reducing agent since it releases electrons and its oxidation number increases from 0 to 2 (Ca→ Ca⁺²). Chlorine, on the other hand, acts as an oxidizing agent (sum of electrons) (Cl → Cl⁻).
