All of the options mentioned involve some form of chemical change, but the correct answer is option 3, which is the production of iodine (I2) from sea-weeds.

Option 1, distillation of sea (salty) water, is a physical process rather than a chemical one. It involves heating the water to separate the water molecules from the dissolved salt particles.

Option 2, crystallization of impure salt (NaCl), is a physical process as well. It involves cooling down a solution of impure salt to allow the salt particles to form orderly crystal structures, separating the impurities from the salt.

Option 4, sublimation of iodine (I2), is a physical process where solid iodine directly changes into a gaseous state without going through the liquid phase.

Option 3 is the correct answer because the production of iodine from sea-weeds involves a chemical process, where chemical reactions take place to convert the organic compounds present in the seaweeds into iodine.