Which one of the following is a redox reaction? Group of answer choices H2O(l) --> H+ (aq) + OH– (aq) K2Cr2O7 (aq) + 2KOH(aq) --> 2K2CrO4 (aq) + H2O(l) Ba2+(aq) + SO42- (aq) --> BaSO4 (s) Na2 CO3 (s) + 2HCl(aq) --> 2NaCl(aq) + CO2 (g) + H2 O(l) 2Na(g) + Cl2 (g) --> 2NaCl(s)

2Na(g) + Cl2 (g) --> 2NaCl(s)

Explanation:

Such type of chemical reaction in which change in oxidation state takes place due to loss and gain of electrons is known as a redox reaction. Such type of the species that lose electron is called reducing agent and the process is known as oxidation because the species is oxidized by losing an electron and thus acts as a reducing agent. Such type of the species that gain electron is called an oxidizing agent and the process is known as reduction because the species is reduced and thus acts as the oxidizing agent. In the given options, only the oxidation number changes in the reaction such as ,  so it is a form of the redox reaction.In this reaction, Na atom changes into ion and the Cl atom converts into ion that means a change in oxidation states occurs 0 to +1 in the case of Na atom and 0 to -1 in the case of Cl atom. In others options, there is no change in the oxidation state so they are not redox reactions.