Assertion: CHCl₃ is stored in dark bottles.

Reason: CHCl₃ is oxidized in dark. 

Assertion is correct but the Reason is incorrect.

The correct answer is OPTION 3 - Assertion is correct but the Reason is incorrect.

CHCl₃ is stored in dark bottles - This is absolutely correct. Chloroform is typically stored in closed, dark-colored (usually amber) bottles, which are filled up to the brim to minimize air exposure. The dark color is intended to prevent light from reaching the chemical, as light provides the energy needed to catalyze a dangerous chemical reaction.

CHCl₃ is oxidized in dark - This is incorrect. Chloroform does not oxidize in the dark. Instead, it is slowly oxidized by air in the presence of light.  When exposed to light and oxygen, Chloroform undergoes a photochemical reaction to form a highly poisonous gas called Phosgene.