Which of the following air pollutants is/are responsible for photochemical smog ? 1. Oxides of nitrogen 2. Ozone 3. Unburnt hydrocarbons 4. Carbon monoxide Select the correct answer from the codes given below :
Consider the following statements : Some amount of chlorides is allowed in drinking water because 1. it helps in killing bacteria. 2. small quantity of chlorides adds to the taste 3. it is not injurious to human health. 4. it is not economical to remove it completely. Which of these statements are correct ?