Write the number of protons, neutrons and electronic configuration of ${}_{19}^{39}\text{K}${19}^{39}\text{K} , ${15}^{31}\text{P}$ . Also state their position in the periodic table.

Name the element which has :

(i) Two shells, both of which are completely filled with electrons ?

(ii) The electronic configuration 2, 8, 3 ?

(iii) A total of three shells with five electrons in its valence shell ?

(iv) A total of four shells with two electrons in its valence shell ?

(v) Twice as many electrons in its second shell as in its first shell ?

In group I of the Periodic Table, three elements X, Y and Z have ionic radii 1.33 Å, 0.95 Å and 0.60 Å respectively. Giving a reason, arrange them in the order of increasing atomic numbers in the group.

Explain why are the following statements not correct:

(i) All groups contain metals and non-metals.

(ii) Atoms of elements in the same group have the same number of electron(s).

(iii) Non-metallic character decreases across a period with increase in atomic number.

(iv) Reactivity increases with atomic number in a group as well as in a period.