Test: JEE Main 35 Year PYQs- The s-Block Elements - JEE MCQ

Both S & E are true and E is the correct explanation of S.

Statement-1 is correct. Statement-2 is also correct but not the correct explanation becuase blue colour of the solution is due to the solvated electrons.

2KO₂ + 2H₂O → 2 KOH + H₂O₂ + O₂.
KO₂ is used as an oxidising agent. It is used as air purifier in space capsules. Submarines and breathing masks as it produces oxygen and remove carbon dioxide.

The alkali metals dissolve in liquid ammonia without evolution of hydrogen. The metal loses electrons and combine with ammonia molecule.

It is ammoniated electron which is responsible for colour.

Sulphate of alkaline earth metal are sparingly soluble or almost not soluble in water whereas BeSO₄ is soluble in water due to high degree of solvation. Be(OH)₂ is insoluble in water but soluble in NaOH.

BeO + 2NaOH→ Na₂BeO₂ + H₂O

Setting of cement is exothermic process which develops interlocking crystals of hydrated silicates

Gypsum is CaSO₄.2H₂O

As we move down the group, the lattice energies of carbonates remain approximately the same. However the hydration energies of the metal cation decreases from Be⁺⁺ to Ba⁺⁺, hence the solubilities of carbonates of the alkaline earth metal decrease down the group mainly due to decreasing hydration energies of the cations  from Be⁺⁺ to Ba⁺⁺.

Permanent hardness of water is due to chlorides and sulphates of calcium and magnesium i.e CaCl₂, CaSO₄, MgCl₂ and MgSO₄.

TIPS/Formulae :
A diamagnetic substance contains no unpaired electron.
H₂ is diamagnetic as it contains all paired electrons

LiCl has partly covalent character. Other halides are ionic  in nature. Lattice energy decreases with increase of ionic radius of cation, anion being the same. Larger is the lattice energy, the higher will be m. pt. hence NaCl will have highest lattice energy.

NOTE : In one electron species, such as H-atom, the energy of orbital depends only on the principal quantum number, n.
Hence answer (d)

i.e. is < 2s = 2p < 3s = 3p = 3d < 4s = 4p ⇒ 4d = 4g

Smaller the size of cation higher is its hydration energy and greater is its ionic mobility hence the correct order is Li⁺ < Na⁺ < K⁺ <  Rb⁺

On the industrial scale hydrogen is prepared from water gas according to following reaction sequence

From the above it is clear that CO is first oxidised to CO₂ which is then absorbed in NaOH.

Calcium carbonate on thermal decomposition gives CaO (Basic oxide) and CO₂ (Acidic oxide)

Very pure hydrogen can be prepared by the action of water on sodium hydride.

The reducing agent loses electron during redox reaction i.e. oxidises itself.

In alkaline earth metals, ionic size increases down the group. The lattice energy remains constant because sulphate  ion is so large, so that small change in cationic size does not make any difference. On moving down the group the degree of hydration of metal ions decreases very much leading to decrease in solubility.

∴ BeSO₄ > MgSO₄ > CaSO₄ > SrSO₄ > BaSO₄

2 mole of water softner require 1 mole of Ca²⁺ ion

So, 1 mole of water softner require 1/2 mole of Ca2+ ion

Thus,   will be maximum uptake

H₂O₂ has oxidizing and reducing properties both.

There  is  extensive  intermolecular hydrogen bonding in  the  condensed phase  instead  of intramolecular H-bonding.

Alkali metals have the lowest ionization energy in each period on the other hand Sc is a d - block element.
Transition metals have smaller atomic radii and higher nuclear charge leading to high ionisation energy.

On heating with excess of air Li, Na and K forms following oxides