Every Book Back multiple-choice question from p-Block Elements-I (12th Standard Chemistry, Samacheer Kalvi) — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
An aqueous solution of borax is
- A. neutral
- B. acidic
- C. basicCorrect
- D. amphoteric
Explanation. Borax undergoes hydrolysis in water to produce sodium hydroxide and boric acid. Since sodium hydroxide is a strong base and boric acid is weak, the resulting solution is basic.
Q2
Boric acid is an acid because its molecule (NEET)
- A. contains replaceable \(H^{+}\) ion
- B. gives up a proton
- C. combines with proton to form water molecule
- D. accepts \(OH^{-}\) from water, releasing protonCorrect
Explanation. Boric acid acts as a Lewis acid in aqueous solution. It does not donate a proton directly but instead accepts a hydroxyl ion from a water molecule, which releases a proton.
Q3
Which among the following is not a borane?
- A. \(B_{2}H_{6}\)
- B. \(B_{3}H_{6}\)Correct
- C. \(B_{4}H_{10}\)
- D. none of these
Explanation. Boranes are compounds containing boron and hydrogen. While \(B_{2}H_{6}\) and \(B_{4}H_{10}\) are well-known examples, \(B_{3}H_{6}\) does not exist as a stable molecular species under normal conditions.
Q4
Which of the following metals has the largest abundance in the earth’s crust?
- A. AluminiumCorrect
- B. Calcium
- C. Magnesium
- D. Sodium
Explanation. Aluminum is the most abundant metallic element found in the earth's crust. It occurs naturally in various minerals, most notably bauxite, which is its primary commercial ore.
Q5
In diborane, the number of electrons that accounts for banana bonds is
- A. six
- B. two
- C. fourCorrect
- D. three
Explanation. Diborane features two three-center two-electron bonds known as banana bonds. Each of these unique bonds involves two electrons shared among three atoms, totaling four electrons for both bridge bonds.
Q6
The element that does not show catenation among the following p-block elements is
- A. Carbon
- B. silicon
- C. LeadCorrect
- D. germanium
Explanation. Catenation is the ability of an element to form long chains or rings of similar atoms. This property decreases down the group, and lead shows practically no tendency for catenation.
Q7
Carbon atoms in fullerene with formula \(C_{60}\) have
- A. \(sp^{3}\) hybridised
- B. \(sp\) hybridised
- C. \(sp^{2}\) hybridisedCorrect
- D. partially \(sp^{2}\) and partially \(sp^{3}\) hybridised
Explanation. In the Buckminsterfullerene molecule, each carbon atom is bonded to three other carbon atoms. This arrangement results in \(sp^{2}\) hybridization for all sixty carbon atoms within the spherical structure.
Q8
Oxidation state of carbon in its hydrides
- A. +4Correct
- B. -4
- C. +3
- D. +2
Explanation. Carbon typically exhibits an oxidation state of +4 in its hydride compounds, such as methane. In these molecules, carbon is more electronegative than hydrogen and shares four pairs of electrons.
Q9
The basic structural unit of silicates is (NEET)
- A. \(SiO_{3}^{2-}\)
- B. \(SiO_{4}^{2-}\)
- C. \(SiO^{-}\)
- D. \(SiO_{4}^{4-}\)Correct
Explanation. The fundamental structural unit found in all silicate minerals is the silicon-oxygen tetrahedron. This unit consists of a central silicon atom surrounded by four oxygen atoms, carrying a net charge of -4.
Q10
The repeating unit in silicone is
Explanation. The repeating unit is identified by observing the structure of the polymeric chain and the chemical groups attached to each silicon atom.
Q11
Which of these is not a monomer for a high molecular mass silicone polymer?
- A. \(Me_{3}SiCl\)Correct
- B. \(PhSiCl_{3}\)
- C. \(MeSiCl_{3}\)
- D. \(Me_{2}SiCl_{2}\)
Explanation. Trimethylsilyl chloride contains only one chlorine atom for bonding, meaning it can only act as a chain terminator. High molecular mass polymers require monomers with at least two reactive sites to continue the chain.
Q12
Which of the following is not \(sp^{2}\) hybridised?
- A. Graphite
- B. graphene
- C. Fullerene
- D. dry iceCorrect
Explanation. Dry ice is the solid form of carbon dioxide, where the carbon atom is \(sp\) hybridized to form linear molecules. In contrast, graphite, graphene, and fullerene all feature \(sp^{2}\) hybridized carbon.
Q13
The geometry at which carbon atom in diamond are bonded to each other is
- A. TetrahedralCorrect
- B. hexagonal
- C. Octahedral
- D. none of these
Explanation. In the diamond crystal lattice, each carbon atom is covalently bonded to four other carbon atoms in a rigid three-dimensional arrangement. This specific spatial orientation is characterized as tetrahedral geometry.
Q14
Which of the following statements is not correct?
- A. Beryl is a cyclic silicate
- B. \(Mg_{2}SiO_{4}\) is an orthosilicate
- C. \(SiO_{4}^{4-}\) is the basic structural unit of silicates
- D. Feldspar is not aluminosilicateCorrect
Explanation. Feldspars are a group of rock-forming minerals that are characterized as three-dimensional framework aluminosilicates. The statement claiming they are not aluminosilicates is therefore incorrect.
Q15
Match items in column - I with the items of column – II and assign the correct code.
Column-I:
A. Borazole
B. Boric acid
C. Quartz
D. Borax
Column-II:
1. \(B(OH)_{3}\)
2. \(B_{3}N_{3}H_{6}\)
3. \(Na_{2}[B_{4}O_{5}(OH)_{4}] \cdot 8H_{2}O\)
4. \(SiO_{2}\)
- A. A-2, B-1, C-4, D-3Correct
- B. A-1, B-2, C-4, D-3
- C. A-1, B-2, C-4, D-3
- D. None of these
Explanation. Matching the chemical names with their correct formulas reveals that borazole is \(B_{3}N_{3}H_{6}\) and boric acid is \(B(OH)_{3}\). Quartz is silicon dioxide, while borax is a hydrated sodium borate salt.
Q16
Duralumin is an alloy of
- A. Cu, Mn
- B. Cu, Al, Mg
- C. Al, Mn
- D. Al, Cu, Mn, MgCorrect
Explanation. Duralumin is a lightweight aluminum alloy used extensively in the aerospace industry. Its primary constituent is aluminum, which is mixed with copper, manganese, and magnesium to enhance its strength.
Q17
The compound that is used in nuclear reactors as protective shields and control rods is
- A. Metal boridesCorrect
- B. metal oxides
- C. Metal carbonates
- D. metal carbide
Explanation. Metal borides, such as those involving boron-10, are highly effective at absorbing neutrons. This property makes them ideal materials for use in nuclear reactor control rods and protective radiation shielding.
Q18
The stability of +1 oxidation state increases in the sequence
- A. Al < Ga < In < TlCorrect
- B. Tl < In < Ga < Al
- C. In < Tl < Ga < Al
- D. Ga < In < Al < Tl
Explanation. Moving down group 13, the s-orbital electrons become increasingly reluctant to participate in chemical bonding. This phenomenon, known as the inert pair effect, makes the +1 oxidation state more stable for heavier elements.
