Give reasons for formation of single covalent bond between two chlorine atoms and a double covalent bond between two oxygen atoms - during formation of a covalent chlorine molecule and formation of a covalent oxygen molecule, respectively.

Give a reason why - in the formation of electrovalent compound - magnesium chloride, one magnesium atom combines with two chlorine atoms to give magnesium chloride. [at. no. Mg=12, Cl=17, ]

'Formation of hydrogen molecule takes place by sharing of electrons'. Give a reason why the molecule of hydrogen is not formed by transfer of electrons.

Draw the atomic orbit structure diagram for formation of a -

(a) water molecule

(b) ammonia molecule

[at. no. H=1, O=8, N=7]