Answer: (1) PCl5 ==> PCl3 + Cl2
Explanation: PCl5 == PCl3 + Cl2 is a redox reaction. In a redox reaction, there will be a change in oxidation number for two elements. The oxidation number of the P is +5 in Pcl5 and it is +3 in PCl3, so the P is reduced. The Cl has an oxidation number of -1 in PCl5, but as a free elements in Cl2 it has an oxidation number of zero, so it is oxidized. Always look for free elements to help identify redox reactions.
