Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shell. It was found that elements A and G combine to form an ionic compound. This compound is added in a small amount to almost all vegetable dishes during cooking. Oxides of elements A and B are basic in nature while those of E and F are acidic. The oxide of D is almost neutral. Based on the above information answer the following questions : (i) To which group or period of the periodic table do the listed elements belong ? (ii) What would be the nature of compound formed by a combination of elements B and F ? (iii) Which two of these elements could definitely be metals ? (iv) Which one of the eight elements is most likely to be found in gaseous state at room temperature ? (v) If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively, write the formula of the compound formed by the combination of C and G.

Based on the clues provided, we can systematically identify the elements and answer the questions:

Identification of Elements

• Elements $A$ to $H$ have the same number of electronic shells, meaning they belong to the same period.
• Elements $A$ and $G$ combine to form an ionic compound added to vegetable dishes during cooking, which is Sodium Chloride ($NaCl$). Thus, $A$ is Sodium ($Na$) and $G$ is Chlorine ($Cl$).
• Since $Na$ (atomic number 11) and $Cl$ (atomic number 17) have three shells ($K, L, M$), all these elements belong to Period 3.
• The elements of Period 3 are:
• $A = Na$ (Group 1, 1 valence electron)
• $B = Mg$ (Group 2, 2 valence electrons)
• $C = Al$ (Group 13, 3 valence electrons)
• $D = Si$ (Group 14, 4 valence electrons)
• $E = P$ (Group 15, 5 valence electrons)
• $F = S$ (Group 16, 6 valence electrons)
• $G = Cl$ (Group 17, 7 valence electrons)
• $H = Ar$ (Group 18, 8 valence electrons)

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Answers to Sub-questions

(i) Group and Period:

• All the listed elements belong to Period 3 of the periodic table.
• Their groups range from Group 1 to Group 18 respectively.

(ii) Nature of compound formed by B and F:

• Element $B$ ($Mg$, a metal) and Element $F$ ($S$, a non-metal) combine to form Magnesium Sulphide ($MgS$).
• The compound is ionic (electrovalent) in nature because it is formed by the transfer of electrons from a metal to a non-metal.

(iii) Two elements that are definitely metals:

• Elements $A$ (Sodium) and $B$ (Magnesium) are definitely metals because they form basic oxides ($Na_2O$ and $MgO$).

(iv) Element most likely to be found in gaseous state:

• Element $H$ (Argon) is a noble gas and is most likely to be found in the gaseous state at room temperature. (Element $G$ / Chlorine is also a gas at room temperature).

(v) Formula of compound formed by C and G:

• Element $C$ has 3 valence electrons (valency = $+3$).
• Element $G$ has 7 valence electrons (valency = $-1$).
• By crossing over their valencies, the chemical formula of the compound is $CG_3$ (which corresponds to Aluminium Chloride, $AlCl_3$).