Assertion (A): In a chemical reaction, the total mass of the products remains the same as that of the reactants.

Reason (R): A chemical reaction involves a simple exchange of partners and no new species are formed.

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): 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): Chemical combination always takes place between two elements.

Reason (R): A single substance is formed in a chemical combination.

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.

Fill in the blanks:

(a) Dalton used symbol …………… for oxygen and …………… for hydrogen.

(b) Symbol represents …………… atom of an element.

(c) Symbolic expression for a molecule is called …………… .

(d) Sodium chloride has two radicals. Sodium is a …………… radical while chloride is a …………… radical.

(e) Valency of phosphorus in PCl₃ is …………… and in PCl₅ is …………… .

(f) Valency of Iron in FeCl₂ is …………… and in FeCl₃ it is …………… .

(g) Formula of iron (III) carbonate is …………… .