These questions are based upon the periodic properties of the elements. Answer the following questions in one or two lines.

(a) Element that has completely filled two shells.

(b) Element that has electronic configuration 2, 8, 2.

(c) Element that has total of three shells with four electrons in its valence shell.

Identify the salts X and Y from the following observations.

(a) Salt X is white in colour. On strong heating, it produces buff yellow residue and liberates reddish brown gas. Solution of salt X produces chalky white insoluble precipitate with excess of ammonium hydroxide.

(b) Salt Y is black in colour. On reacting with conc. HCl, it liberates a pungent greenish yellowish gas which turns moist starch iodide paper blue black.

Calcium, cobalt, nitrogen, magnesium, and silicon are some elements. Using this information complete the following.

(a) …………… is the most reactive metal.

(b) …………… is a metalloid.

(c) …………… is a non-metal.

Give reasons:

(a) Covalent compounds have low melting point.

(b) For covalent bond formation both atoms should have high ionisation.

(c) Covalent bond formation takes place when both atoms should have four or more electron in outermost shell.