Assertion (A): Magnesium phosphate is written as Mg₃(PO₄)₂.

Reason (R): The valencies of magnesium and phosphate are three and two respectively.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Assertion (A): A chemical equation is written to represent molecules.

Reason (R): This is necessary for the law of conservation of mass

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Assertion (A): Hydroxyl radicals (OH•) are considered the "detergents" of the atmosphere.

Reason (R): Hydroxyl radicals are highly reactive and oxidise many pollutants, breaking them down into less harmful substances.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Assertion (A): The concentration of free radicals in the atmosphere is high during the night.

Reason (R): Free radicals are produced by the photolysis of molecules by solar radiation.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.