Name or state the following with reference to the elements of the first three periods of the periodic table.

(a) The noble gas having duplet arrangement of electrons.

(b) The noble gas having an electronic configuration 2, 8, 8.

(c) A metalloid in period 2 and in period 3.

(d) The number of electron shells in elements of period 1, period 2 and period 3.

(e) The valency of elements in group 1 [IA].

(f) The group whose elements have zero valency.

(g) An alkaline earth metal in period 3.

(h) The non-metallic element present in period 3 other than sulphur and chlorine.

(i) A non-metal in period 2 having electronic configuration 2, 6.

(j) An electrovalent compound formed between an alkali metal and a halogen.

(k) A covalent compound formed between an element in period 1 and a halogen.

(l) An alkali metal in period 3 which dissolves in water giving a strong alkali.

(m) A metal in period 3 having valency 3.

(n) The bridge elements of period 3 of group 1 [IA], 2 [IIA] and 13 [IIIA].

(o) The periods which contain the inner transition elements.

(p) The formula of the hydroxide of the element having electronic configuration 2, 8, 2.

(q) The valency of the element in period 3 having atomic number 17.

(r) A non-metal in period 2 which is tetravalent.

(a) The noble gas having duplet arrangement of electrons — Helium

(b) The noble gas having an electronic configuration 2, 8, 8 — Argon

(c) A metalloid in period 2 and in period 3 — Metalloid in period 2 is B (Boron) and in period 3 is Si (Silicon)

(d) The number of electron shells in elements of period 1, period 2 and period 3 — Period 1 —1 shell, Period 2 — 2 shells, Period 3 — 3 shells

(e) The valency of elements in group 1 [IA] — +1

(f) The group whose elements have zero valency — Group 18 or 0 group

(g) An alkaline earth metal in period 3 — Magnesium [Mg]

(h) The non-metallic element present in period 3 other than sulphur and chlorine — Phosphorus [P]

(i) A non-metal in period 2 having electronic configuration 2, 6 — Oxygen [O]

(j) An electrovalent compound formed between an alkali metal and a halogen — Sodium chloride [NaCl]

(k) A covalent compound formed between an element in period 1 and a halogen — Hydrogen chloride [HCl]

(l) An alkali metal in period 3 which dissolves in water giving a strong alkali — Alkali metal is Na and it dissolves in water to give strong alkali - NaOH

(m) A metal in period 3 having valency 3 — Aluminium [Al]

(n) The bridge elements of period 3 of group 1 [IA], 2 [IIA] and 13 [IIIA] — Li & Mg, Be & Al

(o) The periods which contain the inner transition elements — Period 6 and 7

(p) The formula of the hydroxide of the element having electronic configuration 2, 8, 2 —
Since valency of element X is 2+ and valency of OH is 1-

Formula of the compound:

$\text{X}^{2+} \phantom{\nearrow} \text{OH}^{1-} \\[0.5em] \overset{\phantom{2}{2}}{\text{X}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{OH}} \Rightarrow \underset{\phantom{1}{1}}{\text{X}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{OH}} \\[0.5em]$

So, we get the formula as $\bold{X(OH)}\bold{_2}$

As the element with electronic configuration 2,8,2 is Mg, Hence the compound is Mg(OH)₂

(q) The valency of the element in period 3 having atomic number 17 — -1

(r) A non-metal in period 2 which is tetravalent — Carbon [C]