On the surface of polar stratospheric clouds, ClONO2 + H2O -> HOCl + HNO3 is followed by HOCl + HCl -> Cl2 + H2O. Adding the two steps, the overall change and the role of water are

ClONO2 + HCl -> Cl2 + HNO3; water is regenerated and acts as a catalyst

ClONO2 + H2O -> Cl2 + HNO3; HCl is the catalyst

ClONO2 + HCl -> Cl2 + HNO3; water is regenerated and acts as a catalyst

ClONO2 + 2HCl -> 2Cl2 + HNO3; water is consumed

ClONO2 + HCl -> HOCl + NO2 + Cl; water is a product

JEE Advanced levelSingle correct optionDifficulty 3 of 3ev089

On the surface of polar stratospheric clouds, $ClONO X_{2} + H X_{2} O HOCl + HNO X_{3}$ is followed by $HOCl + HCl Cl X_{2} + H X_{2} O$ . Adding the two steps, the overall change and the role of water are

A $ClONO X_{2} + H X_{2} O Cl X_{2} + HNO X_{3}$ ; HCl is the catalyst
B $ClONO X_{2} + HCl Cl X_{2} + HNO X_{3}$ ; water is regenerated and acts as a catalyst
C $ClONO X_{2} + 2 HCl 2 Cl X_{2} + HNO X_{3}$ ; water is consumed
D $ClONO X_{2} + HCl HOCl + NO X_{2} + Cl$ ; water is a product

Sum:

ClONO X_{2} + H X_{2} O + HOCl + HCl HOCl + HNO X_{3} + Cl X_{2} + H X_{2} O

. HOCl and

H X_{2} O

appear on both sides and cancel, giving

ClONO X_{2} + HCl Cl X_{2} + HNO X_{3}

(balanced: 2 Cl, 1 N, 3 O, 1 H each side). Water is consumed in step 1 and regenerated in step 2, and HOCl is only an intermediate.