Here we need to determine which of the following is an exothermic reaction. For D we're going to have steam condensing, so just make sure you see steam condensing there. Now it says if we look at the options, we have CL2 burning. Now burning usually connotes that we're breaking something down. You know you burn a piece of wood, it breaks it down. You're breaking bonds, so that would be indicative of an endothermic reaction, not an exothermic reaction. Remember exothermic is bond forming, not bond breaking.
Next reaction in a cold pack? Well, a cold pack feels cold to the touch, but we said earlier that exothermic reactions which release heat feel warm to the touch. So a hot pack or heating pack would be an exothermic reaction, dry ice subliming. So remember, if you're subliming, you're going from a, let's see, you're going from a solid to a gas. But remember, we're talking about forming bonds. We want to go do deposition where we're going from a gas to a solid.
The only one that makes sense in terms of an exothermic process is steam condensing. We're going from a gas to a liquid, so we're forming bonds. So remember, exothermic reactions are bond forming, heat releasing reactions, meaning D is the only option that makes the most sense.