Question

Which is a redox reaction?

A) 2KBr + F2 ---> 2KF + Br2
B) 2HCL + Mg(OH)2 --> 2HOH + MgCl2
C) 2NaCl + H2SO4 --> Na2SO4 + 2HCl
D) Ca(OH)2 + Pb(NO3)2 --> Ca(NO3)2 + Pb(OH)2

I know the answer is A, but confused as to why that is. Can someone explain this for me? Thanks.

Answer 1

You have to look at the oxidation states of each atom in the reaction. Since redox reactions involve the transfer of electrons from one element to another, 2 elements need to have oxidation state changes.
option a is the only option that has a change in oxidation sates. Fluorine goes from 0 to -1 indicating that it gained electrons (got reduced) while bromine goes from -1 to 0 indicating it loses electrons (got oxidized).
(2Br⁻→Br₂+2e⁻ and F₂+2e⁻→2F⁻).

I hope this helps. Let me know if anything is unclear.