31 Year NEET Previous Year Questions: The s-Block Elements - NEET

Within a group, ionic radius increases with increase in atomic number. The melting points decrease down the group due to weakning of metallic bond. The electronegativity and the 1^st ionization energy also decreases down the group.

Within a period, the atomic size decreases from left to right.Further atomic size increases down the group. Hence the correct order is   i,e. Na > Mg > Li > Be.

Because of larger size and smaller nuclear charge, alkali metals have low ionization potential relative to alkaline earth metals.

Washing soda is Na₂ CO₃. 10 H₂O.

Ca(20) = 1s²2s²3p⁶ 3s²3p⁶ 4s² = [Ar] 4s²

Out of Li, Na, K and Rb, Rb reacts fastest with water. The rate of reaction increases down the group.

Atomic size of K⁺ > Ca²⁺ > Mg²⁺ and that of Cl^– > F^–. Therefore, Mg²⁺/Cl^– ratio has the minimum value.

A cation is always much smaller than the corresponding atom(with increase in positive charge, atomic particles move close to each other), whereas an anion is always larger than the corresponding atom(with increase in negative charge, size increases to minimise the effect of steric repulsion). 

Mixture of K₂CO₃ and Na₂CO₃ is called fusion mixture

Ca and CaH₂ both react with H₂O to form H₂ gas,

whereas K gives H₂ while KO₂ gives O₂ and H₂O₂

Similarly, Na gives H₂ while Na₂ O₂ gives
H₂O₂

Likewise Ba gives H₂ while BaO₂ gives H₂O₂

MgO. N₂O₅ is strongly acidic, ZnO and Al₂ O₃ are amphoteric, therefore, MgO is most basic.

Ca²⁺ ions is an essential element for the contraction of muscles.

Be(OH)₂ is amphoteric, but the hydroxides of other alkaline earth metals are basic. The basic strength increases gradually.

Sodium is obtained by electrolytic reduction of its chloride. Melting point of chloride of sodium is high (803°C) so in order to lower its melting point(600°C), calcium chloride is added to it.

Gypsum is CaSO₄. 2H₂O and plaster of Paris i s (CaSO₄)₂ .H₂O. Therefore gypsum contains a lower percentage of calcium than plaster of Paris.

MgSO₄ is the only alkaline ear th metal sulphate which is soluble in water and for solubility hydration energy should be greater than lattice energy i.e hydration energy > lattice energy

Calcium is obtained by electrolysis of a fused mass consisting six parts calcium chloride and one part calcium fluoride at about 700°C in an electrolytic cell.

As Cs⁺ ion has larger size than Li⁺ and I^– has larger size than F^–, therefore maximum distance between centres of cations and anions is in CsI.

In Castner process, for production of (Na) Sodium metal, Sodium hydroxide (NaOH) is electrolysed at temperature 330ºC.

The given properties coincide with CaCO₃

Hydration enthalpies of alkali metal ions decreases with the increase in ionic radii as we move down the group.

Therefore, smaller is the mass of hydrated species higher is the ionic mobility in the aqueous solution.

Thus, the order for ionic mobility of ions is

Rb⁺ > K⁺ > Na⁺ > Li⁺

As the basicity of metal hydroxides increases down the group from Be to Ba, the thermal stability of their carbonates also increases in the same order. Further group 1 compounds are more thermally stable than group 2 because their hydroxide are much basic than group 2 hydroxides therefore, the order of thermal stability is BeCO₃ < MgCO₃< CaCO₃< K₂CO₃.

The solubility of sulphates of alkaline earth metals decreases as we move down the group from Be to Ba due to the reason that ionic size increases down the group. The lattice energy remains constant because sulphate  ion is so large, so that small change in cationic sizes do not make any difference.
Thus the order:

Smaller the ion more is its ionic mobility in aqueous solution. Ionic radii of the given alkali metals is in the order Na⁺ < K⁺ < Rb⁺ < Cs⁺ and thus expected ionic mobility will be in the order Cs⁺ < Rb⁺ < K⁺ < Na⁺. However due to high degree of solvation (or hydration) because of lower size or high charge density, the hydrated ion size follows the order Cs⁺ < Rb⁺ < K⁺ < Na⁺ and thus conductivity order is Cs⁺ > Rb⁺ > K⁺ > Na⁺ i.e. option (b) is correct answer.

The stability of alkali metal hydrides decreases from Li to Cs. It is due to the  fact that M–H bonds becomes weaker with increase in size of alkali metals as we move down the group from Li to Cs. Thus the order of stability of hydrides is LiH > NaH > KH > RbH > CsH i.e. option (d) is correct answer.

NaOH is a strong alkali. It combines with acidic and amphoteric oxides to form salts.
Since CaO is a basic oxide hence does not reacts with NaOH.

Be²⁺ is very small, hence its hydration enthalpy is greater than its lattice enthalpy (At. Nos. Mn = 25, Fe = 26, Co = 27, Ni = 28)

Lattice energy decreases more rapidly than hydration energy for alkaline earth metal hydroxides.

∴ Correct choice : (b)

Melting points of halides decreases as the size of the halogen increases. The correct order is CaF₂ > CaCl₂ > CaBr₂ > CaI₂

Active ingredient in bleaching powder for bleaching action is Ca (OCl)₂

(A) Plaster of paris = 

(B) Epsomite = MgSO₄.7H₂O
(C) Kieserite = MgSO₄.H₂O
(D) Gypsum = CaSO₄.2H₂O

All the alkali metals when heated with oxygen form different types of oxides for example lithium forms lithium oxide (Li₂O), sodium forms sodium peroxide (Na₂O₂), while K, Rb and Cs form their respective superoxides.

All a lkali  metal salts are ionic (except Lithium) and soluble  in water due to the fact that cations get hydrated by water molecules. The  degree of hydration depends upon the size of the cation. Smaller the size of a cation, greater is its hydration energy.
Relative ionic radii :

Relative ionic radii in water or relative degree of hydration:

Tertiary halide can show ionic reaction with MF so, MF should be most ionic for reaction to proceed forward. Hence ‘M’ should be ‘Rb’.

At the cathode, since the discharge + ions is lower than that of H⁺ ions on the mercury, cathode, so Na⁺ ions are discharged while H⁺ ions remain in the solution.