Which of the following statements about acid rain are correct?

AIt converts marble ( $CaCO X_{3}$ ) into calcium sulphate with release of $CO X_{2}$ .
BRain with pH below 5.6 is called acid rain.
CUnpolluted rain has a pH of exactly 7.0 because no gas dissolves in it.
DOxides of nitrogen contribute to it through the formation of $HNO X_{3}$ .

Answer: A, B, D

The threshold for acid rain is pH 5.6, the value for rain equilibrated with atmospheric

CO X_{2}

NO X_{2}

yields

HNO X_{3}

and sulphuric acid attacks marble to give

CaSO X_{4}

and

CO X_{2}

. Unpolluted rain is not exactly neutral because

CO X_{2}

dissolves, so the third statement is false.