Which of the following is responsible for depletion of ozone layer in the upper strata of the atmosphere?

Freons 

The correct answer is option 4. Freons.

Freon-1 (CFCl₃) and freon-12 (CF₂Cl₂) are two examples of stable and chemically inert fluorocarbons released as propellants in aerosol spray cans, refrigerators, and other products. They float in the atmosphere unaffected and eventually penetrate the stratosphere because they have no reaction to whatever substance they come into contact with. There, they take up UV rays and decompose, releasing free atomic chlorine that causes ozone to degrade. This causes the ozone layer to thin down.