The correct option is B The oxidation state of Carbon increases.
Ethylene undergoes reduction with iodine to form 1,2-Diiodoethane
CH2=CH2+I2→I−CH2−CH2−I
(Ethylene) (Iodine) (1,2-Diiodoethane)
Now that we have figured the product, check the validity of each of the given options. Clearly Iodine is more electronegative than Carbon. So the electrons in the C−I bond will be closer to the Iodine atom. Hence, Iodine will be assigned a -1 oxidation state. Overall, the molecule is neutral. In ethylene, each Carbon atom has -2 oxidation state while in 1,2-Diiodoethane, each Carbon has -1 oxidation state.
The oxidation state of Carbon increases.