Which of the following options is true about smog ?
A. Generally formed in winter
B. Made up of smoke and fog
C. Causes ozone depletion
D. Causes asthma and cough

Correct option is C

The correct answer is A, B and D.
(A) Generally formed in winter: This is not entirely true. While winter smog (caused by temperature inversions trapping pollutants) is a type of smog, photochemical smog, which is more common in summer, also exists.
(B) Made up of smoke and fog: While smoke and fog can be components of smog, it's not just a simple mixture. Smog is a complex combination of pollutants, including ozone, nitrogen oxides, and volatile organic compounds.
(C) Causes ozone depletion: This is incorrect. Smog actually contributes to ground-level ozone formation, which is harmful to human health and the environment. The ozone layer in the upper atmosphere protects us from harmful UV radiation, and its depletion is caused by different chemicals like chlorofluorocarbons (CFCs).
(D) Causes asthma and cough: This is true. Smog exposure can irritate the respiratory system and trigger asthma attacks, coughing, and other respiratory problems.