Given the balanced equation representing a reaction:
2kclo3(s) ==> 2kcl(s) + 3o2(g)
the oxidation state of chlorine in this reaction changes from
(1) -1 to +1 (3) +1 to -1
(2) -1 to +5 (4) +5 to -1

Oxidation # of Cl in Potassium Chlorate: 
    Let x= oxidation state of Cl
               
                (+1) + (x) + (-2 * 3) = 0
                                     (x) - 5 = 0
       ∴                                    x = +5

Oxidation State of Cl in Potassium Chloride
Let oxidation state of Cl = y
                           KCl
                  (+1) + (x) = 0
                               x = 0

Thus Cl goes from +5 to -1 (option 4) [REDUCTION]

Note: oxidation of :
                O is alway -2 unless told otherwise by instructions
                K is +1