The S-block Elements

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Correct Option (iii)

Li due to its small size it has a high value of hydration enthalpy. Due to the high hydration enthalpy of Li atom, it is the strongest reducing agent in the aqueous medium.

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Correct Option (i)

The reactivity of alkali metals increases on moving down the group. So, Li is least reactive. It will react with water least vigorously.

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Correct Option (iv)

In alkali metals, on going down the group, as the metallic strength decreases, melting point  decreases. Thus, Cs has the lowest melting point and melts at 30°C.

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In the solid state BeCl₂ has a polymeric chain like structure. Be atom is surrounded by four Cl atoms among which two of them are bonded through covalent bond and other two are through co-ordinate bond. Structure of BeCl₂ is given by structure A.

In gaseous state beryllium chloride exists as dimer (Be₂Cl₄) which dissociates to the monomer at about 1200 K temperature which is linear in structure.

Structure of BeCl₂ in gaseous state is given by the structure B.

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The flame is due to the excitation of the electron from its higher energy state to the lower energy states. Due to the small atomic and ionic size of beryllium and magnesium, electrons are tightly bound to the atom. The electrons of Be and Mg does not gain excitation from the energy provided by the flame. Hence they do not show any flame in the flame test.

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The lewis structure of O₂^– ion is,

Oxygen atom having no charge has 6 electrons, so its oxidation number is zero. Oxygen atoms containing −1 charge have 7 electrons, so its oxidation number is −1. The average oxidation state of oxygen in this ion is, =1/2

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In the Solvay process, carbon dioxide is transferred through a concentrated solution of ammoniacontaining sodium chloride, which forms ammonium carbonate followed by ammonium hydrogen carbonate. The chemicals in ammonium hydrogen carbonate are different and are heated to form sodium carbonate. NH₃ is found in a solution containing NH₄Cl that is heated and treated with Ca (OH)₂? The reaction of (NH₄)2CO₃ with NaCl provides two products, Na₂CO₃ and NH₄Cl both soluble in water which do not shift to the right balance.

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Ionic compounds are formed from the alkali metals due to their large ionic size and low ionization enthalpy. Thus, they are soluble in water. But, due to the small ionic size, high ionization enthalpy, and high electronegativity of lithium, it forms compounds of covalent nature and thus, are soluble in organic solvents.

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BeSO₄ and MgSO₄ readily soluble in water while CaSO₄, SrSO₄ and BaSO₄ are insoluble The greater hydration enthalpy of Be²⁺ and Mg²⁺ ions overcome the lattice enthalpy factor and therefore, their sulfates are soluble.