Test: MCQs (One or More Correct Option): The p-Block Elements | JEE Advanced - JEE MCQ

Because of high melting point (2050ºC), pure alumina cannot be electrolysed. Hence a mixture of alumina, cryolite (m.p. 1000ºC) and calcium fluoride (to lower the temperature of the melt) is electrolysed at about 900ºC.
NOTE : The function of cryolite is to increase the electrical conductivity of the electrolyte, and to lower the temperature of the melt.

NH₄NO₃ ——→ N₂O + 2H₂O
NH₂OH.HCl + NaNO₂ ——→ N₂O + NaCl + 2H₂O

NH₃ and CF₂Cl₂ (freon-12) are used as refrigerants.

To make the fused mixture very conducting and to reduce the temperature of the melt.

Silicon is used in solar cells.

Sodium nitrate on decomposition upto 500^oC gives NaNO₂ and oxygen.

While at higher temperature (i.e. above to 800°C), NaNO₂ further decomposes into  Na₂O, N₂ and O₂.

The four atoms in a P₄ molecule are situated at the corners of a tetrahedron. There are six P - P single bonds with PPP bond angle equal to 60^o. Each phosphorus has a lone pair of electrons.

2NH₃ + OCl–→ NH₂.NH₂ + H₂O + Cl^–

When ammonium salt NH₄NO₃ or NH₄NO₂ (ammonium salts are colourless) is boiled with excess of NaOH, ammonia (NH₃) gas is evolved as follows:

NH₄NO₂ + NaOH → NaNO₂ + NH₃ + H₂O
NH₄NO₃ + NaOH → NaNO₃ + NH₃ + H₂O

The NH₃ gas evolved is non-flammable gas.
When the gas evolution ceases we are left with NaNO₂ or NaNO₃ in solution.
These salts get reduced when Zn is added to this solution containing salt (NaNO₂ or NaNO₃) and excess NaOH and NH₃ gas is evolve.

Thus the colourless salt [H] is either NH₄NO₂ or NH₄NO₃.
Thus (a) and (b) are correct answers. [NOTE : NaCl formed has no reaction with NaOH]

(a) Diamond is harder than graphite.
(b) Graphite is good conductor of electricity as each carbon is attached to three C-atoms leaving one valency free, which is responsible for electrical conduction, while in diamond, all the four valencies of carbon are satisfied, hence insulator.
(c) Diamond is better thermal conductor than graphite.
Whereas electrical conduction is due to availability of free electrons; thermal conduction is due to transfer of thermal vibrations from atom to atom. A compact and precisely aligned crystal like diamond thus facilitates fast movement of heat.
(d) In graphite, C – C bond acquires double bond character, hence higher bond order than in diamond.

Ozone is diamagnetic in nature (due to presence of paired electron) and both the O – O bond length are equal. It has a bent structure.

Balanced chemical equation is

H₃BO₃ does not undergo self ionization. However, it acts as a weak acid in water (hence it is a weak electrolyte in water).

Addition of cis-diols (e.g., ethylene glycol) to aqueous solution of orthoboric acid leads to complex formation, thus acidity of aqueous solution of orthoboric acid is increased.

Number of Cl = O bonds in (ii) and (iii) together is 3 Number of lone pairs on Cl in (ii) and (iii) together is 3 Hybridisation of Cl in all the four is sp³
Strongest acid is HClO₄ (iv)

(CH₃)₂SiCl₂ form linear polymer on hydrolysis and (CH₃)₃SiCl is a chain terminator.

Structure of borax

Correct formula of borax is Na₂[B₄O₅(OH)₄].8H₂O
(A) Borax has tetranuclear.  [B₄O₅(OH)₄]^2– unit
(B) Only two 'B' atom lie in same plane
(C) two Boron are sp² and two are sp³ hybridised.
(D) one terminal hydroxide per boran atom