Short Answer Type
Long Answer Type(a) Occurence of boron and uses:
Boron is not found free in nature. It mainly occurs as bortes and orthoboric acid. The important minerals of boron are:
1. Borax (Tincal) Na2B4O7 . 10H2O
2. Colemanite Ca2B6O11 . 5H2O
3. Kernite Na2B4O7.2H2O
4. Boric acid H3BO3
In India borax occurs in Puga valley (Ladakh) and Sambhar Lake (Rajasthan). The abundance of boron in the earth crust is less than 0.0001% by mass. There are two isotopic forms of boron l0B(19%) and 11B(81 %).
(b) Occurrence of aluminium and uses:
Aluminium does not occur freely in nature, but its compounds (minerals) are widely distributed in nature. It is the third most abundant element (next to oxygen and silicon). Some minerals of aluminium are
1. Oxides.
(i) Corundum (Al2O3)
(ii) Diaspore (Al2O3H2O)
(iii) Bauxite (Al2O3.2H2O)
2. Fluoride, Cryolite Na3AlF6
3. Silicate.
(i) Feldspar (KA1 Si3O8)
(ii) Kaolin or slate (K2O.2H2O.3Al2O3.6SiO2)
4. Basic sulphate Alunite or Alum stone K2SO4 Al2(SO4)3.4Al(OH)3
The important ore of aluminium is bauxite. In India aluminium is found as mica in Madhya Pradesh, Karnataka, Orissa and Jammu.
(c) Occurrence of gallium, indium and thallium These are less abundant elements in nature.
Discuss the characteristics of group 13 elements in terms of:
(i) Atomic and ionic radii
(ii) ionisation enthalpy
(iii) Density, melting point and boiling points.
Short Answer TypeLong Answer TypeExplain the following:
(i) Boron is trivalent
(ii) Boron and aluminium tend to form covalent compounds.
Discuss the pattern of variation in the oxidation states of B(Boron) to Tl(Thallium).
Or
What is inert pair effect? Illustrate it with reference to Boron family.
Short Answer TypeStandard electrode potential values 
and that of 
is +1.26 V. Predict about the formation of M3+ ion in solution and compare the electropositive character of the two metals.
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