For an element, Z = 9. The valency of this element will be:

The atomic numbers of four elements A, B, C and D are 12, 13, 15 and 3 respectively. The element which cannot form a cation is:

The number of valence electrons in a sulphide ion, S^2-, is:

Four elements W, X, Y and Z contain 8, 11, 9 and 17 protons per atom respectively. The element which cannot form an anion is most likely to be:

The four atomic species can be represented as follows. Out of these, the two species which can be termed isobars are:

A.

B.

C.

D.