The correct answer for the contents of an airbag used for the safety of a car driver is option 2: Sodium azide.

Sodium azide is a solid compound that is commonly used in airbags. When an accident occurs and the car`s sensors detect a sudden deceleration, sodium azide is rapidly ignited. This chemical reaction produces nitrogen gas, which inflates the airbag within milliseconds.

Option 1, sodium bicarbonate, is incorrect as it is not a component of airbags. Sodium bicarbonate is commonly known as baking soda and is used in cooking and as an antacid.

Option 3, sodium nitrite, is also incorrect as it is not used in airbags. Sodium nitrite is primarily used as a food preservative and as a curing agent in meat products.

Option 4, sodium peroxide, is also incorrect as it is not an ingredient in airbags. Sodium peroxide is a strong oxidizer that is commonly used in laboratories and industries for various purposes.

To summarize, the correct answer is option 2: Sodium azide, as it is the compound that undergoes a chemical reaction to rapidly inflate the airbag and provide safety for the car driver in case of an accident.