There are four elements P, Q, R and S having atomic numbers of 4, 18, 10 and 16 respectively. The element which can exhibit covalency as well as electrovalency will be:

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.

The atomic number of an element X is 8 and that of element Y is 4. Both these elements can exhibit a valency of:

The isotopes of an element contain: