CBSE Class 9 Answered
(a) Atomicity :-
Number of atoms in single molecule of an element is called as atomicity. e.g. atomicity of oxygen gas is 2.
(b) Anion :-
A negatively charged ion is called anion. e.g. SO42-
(c)Molecular Mass :-
The molecular mass of substance is the relative mass of its molecule expressed in atomic mass unit(u). It is
equal to the sum of the atomic masses of all the atoms present in one molecule of the substance.e.g. one
molecule of water (H2O) contains two atoms of hydrogen and one atom of oxygen.
(d) Relative Formula Mass :-
The formula mass of a substance is the sum of atomic masses of all atoms in a formula unit of a compound
or Formula Mass is used for substances whose constituent particles are ions.
(e) Cation :-
A positively charged ion is called as cation. e.g. Na+