Fill in the blanks:

(a) A symbol represents …………… of an element.

(b) An atom is neither created nor destroyed during a …………… .

(c) …………… are positively charged ions.

(d) Total number of atoms of all the elements present in Al₂O₃ is …………… .

(e) A …………… is the symbolic representation of a chemical reaction using symbols and formulae of the substances taking part in the reaction.

Write 'true' or 'false' for the following and correct the false statements.

(a) When an atom gains one or more electrons, it becomes positively charged.

(b) The valency of nitrogen in ammonia gas is 3.

(c) The sulphide ion is a polyatomic ion.

(d) The nitrate ion is represented as NO₂^-.

(e) The element cobalt is represented as CO.

Name the following:

(a) A polyatomic positive ion.

(b) The substances written on the left side of an arrow in an equation.

(c) The substances which are formed during a chemical reaction.

(d) An unbalanced chemical equation.

(e) An atom or group of atoms that behave as a single charged unit.

(f) A substance used to increase the rate of reaction.

Write the names of the following ions:

(a) HCO₃^-

(b) MnO₄^-

(c) N^3-

(d) Cr₂O₇^2-