Arranging the given elements into different groups and periods in order of their increasing atomic numbers we have:

Since the metallic character decrease along a period from left to right, therefore, metallic character increases in the order: Ge < Ga < Ca < K. .
Since metallic character increases down the group from top to bottom, therefore Ca is more metallic than Mg.
Combining above two results, the overall metallic character increases in the order: Ge < Ga < Mg < Ca < K.

Since the atomic number of the element X is 19, so its electronic configuration is 2, 8,8, 1 and hence the element X in the metal potassium. Further the atomic number of the element Y is 17, so its electronic configuration is 2, 8, 7 and hence the element Y is the non-metal chlorine. Now we know that metals lose the valence electrons and the nonmetal accept the electrons lost by the metals to acquire the stable electronic configuration of the nearest noble gas. As a result, metals form positive ions (cations) and non-metals form negative ions (anions) and an ionic bond is formed between the positively and the negatively charged species. In other words, the formula of the product formed between K and Cl is K⁺ Cl^- and its electron dot structure is

The nature of bond is ionic bond.

Since elements 1 - 3 electrons in the valence shell are metals, those having 4 valence electrons may be non-metals, metalloids or may even be metals those having 5-8 valence electrons are non-metals. Thus elements a), b) and d) are metals while element c) is a non-metal.

(a) Atomic radii decrease along a period from left to right due to increasing nuclear charge. Thus the atomic radii of Li, Be, F and N increase in the order: F<N<Be<Li.
(b) Atomic radii increase in a group from top to bottom due to the corresponding increase in the number of filled electronic shells. The atomic radii of Cl, At, Br and I increase in the order : Cl<Br<I<At.

The electronic configuration is related to the position of element in Periodic table. The numbers of electrons in outermost shell show the number of group and the number of shells shows the number of periods.