p-Block Elements and Their Uses

Alloy 1050 contains 99.5% of aluminium by mass, alloy 1060 contains 99.6% aluminium by weight, alloy 1100 contains 99.0% aluminium by mass, alloy 1199 contains 99.9% of aluminium by weight and alloy 2014 contains 90.9% of aluminium by mass. Hence, alloy 1199 has the maximum percentage of aluminium by weight.

Standard electrode potential values for two half cell reactions suggest that aluminium has high tendency to make Al³⁺(aq) ions, whereas Tl³⁺ is not only unstable in solution but is a powerful oxidising agent also. Thus, Tl⁺ is more stable in solution than Tl³⁺. Aluminium being able to form Al³⁺ ions easily, is more electropositive than thallium.

P. Due to non-availability of d orbitals, boron is unable to expand its octet. Therefore, the maximum covalence of boron cannot exceed 4. Al, Ga, In and Tl have vacant d orbitals and form such type of ions.
Q. Alclad is a trademark of Alcoa used as a generic term to describe corrosion-resistant aluminium sheet formed from high-purity aluminium surface layers metallurgically bonded to high-strength aluminium alloy core material.
R. Boron fiber exhibits a unique combination of high strength, high modulus and large diameter. Boron fibres are used in making bullet-proof vest and light composite material for aircraft.

Thallium tends to oxidize to the +3 and +1 oxidation states as ionic salts. The +3 state resembles that of the other elements in thallium's group (boron, aluminum, gallium, indium). Thallium represents +1 oxidation state due to the inert pair effect.
Hence, Tl(OH) and TlBr are more stable complexes than TlN₃ and TlCl₃.

P. Kernite (Na₂B4O₇.4H₂O) is the mineral of boron.
Q. There are two isotopic forms of boron ¹⁰B (19%) and ¹¹B (81%).
R. Boron (2427 KJ/mol) has higher second Ionization enthalpy than aluminium (1816 KJ/mol).

Arachno-borane has the structural formula- B_nH_n+6.

Green coloured glass is made by the addition of CuO.

The correct sequence of codes is P - 3, Q - 1, R - 4, S – 2.

P. The melting and boiling points of gallium are 29.8^oC and 2204^oC whereas the melting and boiling points of indium are 156^oC and 2072^oC respectively.

Q. Tusionite is a rare colourless to transparent to translucent yellow brown trigonal borate mineral with chemical formula-MnSn(BO₃)₂. The mineral is composed of 18.86% manganese, 40.76% tin, 7.42% boron, and 32.96% oxygen.

R. Gallium and its derivatives have only found applications in recent decades. Gallium arsenide has been used in semiconductors, in amplifiers, in solar cells (for example in satellites) and in the manufacturing of tunnel diodes for FM transmitter circuits.

Alloy 7116 is composed of 93.87-95.17% Al, 0.15% Si, 0.3% Fe, 0.5-1.1% Cu, 0.05% Mn, 0.8-1.4% Mg, 4.2-5.2% Zn, 0.05% V, 0.05% Ti and 0.03% Ga.

Second ionization enthalpy of N = 2856 KJ/mol
Second ionization enthalpy of P = 1903 KJ/mol
Second ionization enthalpy of Al = 1816 KJ/mol
Second ionization enthalpy of Si = 1577 KJ/mol
Hence, regarding N, Al, P and Si, the second ionization enthalpy follow the order of N>P>Al>Si.

Caro’s acid (H₂SO₅) is monobasic on account of the presence of one replaceable hydrogen atom. The presence of one replaceable hydrogen atom is explained by the example of potassium peroxymonosulfate (KHSO₅) which is formed by the reaction of H₂SO₅ with alkali. It is the potassium acid salt of peroxymonosulphuric acid and is widely used as an oxidising agent.

Boron (B) is metalloid and has melting point of 2076^oC. Al has melting point 660^oC, Ga has melting point of 29.8^oC, In has the melting point of 156^oC and Tl has the melting point of 303^oC. 
Hence, boron has the highest melting point among the given elements.

P. Decaborane-14 has ten boron atoms. This number is two short of being able to form a regular icosahedron geometry. Orthocarborane (B₁₀C₂H₁₀R₂) has 12 corners and 20 faces and has regular icosahedron geometry.
Q. [SiF₆]^2– is known whereas [SiCl₆]^2– is not. The main reasons are: (i) six large chloride ions cannot be accommodated around Si⁴⁺ due to limitation of its size. (ii) interaction between lone pair of chloride ion and Si⁴⁺ is not very strong.
R. p-Type semiconductors are made by the doping of Si atoms in group 15 elements and n-Type semiconductors are made by the doping of Si atoms in group 13 elements.

The ionic radii of B³⁺ = 27 pm, Al³⁺ = 53.5 pm, Si⁴⁺ = 40 pm and N^3- = 171 pm. Hence, the ionic radii of B³⁺, Al³⁺, Si⁴⁺ and N^3- varies in the order of N^3- > Al³⁺ > Si⁴⁺ > B³⁺.

BF₃ is a weaker Lewis acid than BCl₃ because of the greater pπ-pπ back bonding effect in BBr₃. BF₃ and BBr₃ both have sp² hybridisation with trigonal planar geometry.