This set of Class 11 Chemistry Chapter 11 Multiple Choice Questions & Answers (MCQs) focuses on “p-Block Elements – Important Compounds of Boron”.
1. Diborane is a ____________
a) monomer
b) dimer
c) trimer
d) polymer
View Answer
Explanation: Borane does not exist so it exists as a dimer in the form of diborane. The structure of diborane is in a complex state and it has an sp3 hybrid state. In diborane, a banana bond exists which is 3 Centre 2 electrons Bond.
2. The complete combustion of diborane is ____________
a) endothermic
b) exothermic
c) there is no change in energy
d) depends on the reaction
View Answer
Explanation: One of the main important uses of diborane is that it is used in rockets as a propellant. The complete combustion of diborane is highly exothermic. Though, the complete combustion in rockets isn’t possible due to the production of boron monoxide.
3. Does Boron occur in a free state?
a) No
b) Yes
c) Sometimes
d) May not be
View Answer
Explanation: Boron does not occur in a free state, it occurs in the form of some compounds like borax, Kernite, orthoboric acid. Elemental Boron can be obtained through many methods like the reduction of boric for oxide with highly electropositive metals or by the reaction of Boron halides with hydrogen.
4. The chemical name of borax is a ____________
a) sulphur tetraborate decahydrate
b) sodium tetraborate decahydrate
c) sodium pentaborate nano hydrate
d) sodium hexa borate hexahydrate
View Answer
Explanation: The chemical name of borax is sodium tetraborate decahydrate, its chemical formula is Na2B4O7.10H2O, and it is made up of two atoms of sodium, four atoms of Boron, seven atoms of Oxygen and 10 moles of water.
5. What is the colour of borax bead in the basic radical chromium test?
a) White
b) Brown white
c) Green
d) Blue
View Answer
Explanation: Borax bead is used for the detection of coloured basic radicals under the name borax bead test. The action of heat on borax gives Sodium metaborate and boric anhydride which form a Glassy bead and when it reacts with the basic radical, gives out a colour. For chromium, it is green in colour.
6. Tincal is ____________
a) alum
b) aluminium
c) boric acid
d) borax
View Answer
Explanation: Tincal is also known as the pure and natural form of borax, its chemical formula is given by Na2B4O7.10H2O, it is one of the important minerals of boron as boron does not occur in the free state, it is an ore of boron that exists in the form of hydrated sodium borate.
7. What do we get upon heating or orthoboric acid at last?
a) Metaboric acid
b) Tetraboric acid
c) Borax
d) Boron trioxide
View Answer
Explanation: When we heat orthoboric acid at 273 K, we get metaboric acid. Again by heating metaboric acid at 473 K, we get tetraboric acid further heating tetraboric acid to Red Hot we finally get boron trioxide as a final product which is boric anhydride.
8. Orthoboric acid is a weak monobasic Lewis acid.
a) True
b) False
View Answer
Explanation: When 1 mole of orthoboric acid combines with two moles of water it gives an anion of boron hydroxide and 1 hydronium ion, it proves that orthoboric acid is a weak monobasic acid as well as a lewis acid, so the above statement is considered to be true.
9. What is the chemical formula of the mineral colemanite?
a) CaB6O.5H2O
b) Na2B4O7.10H2O
c) Ca2B6O.5H2O
d) Na4O7.10H2O
View Answer
Explanation: The chemical formula of the colemanite is Ca2B6O.5H2O. 5H2O and it is given that borax occurs naturally as tincal in dried up lakes it is also obtained by boiling of mineral colemanite with a solution of sodium carbonate.
10. Which of the following salt has an outcome of blue colour as a result of a borax bead test?
a) Nickel sulphate
b) Cobalt sulphate
c) Ferrous sulphate
d) Chromium sulphate
View Answer
Explanation: Cobalt sulphate on heating gives cobalt oxide and sulphur trioxide, further cobalt oxide is combined with boric anhydride which gives cobalt metaborate which is a blue coloured Bead, the colours of iron, chromium and Nickel are green, green and brown respectively.
11. What is inorganic benzene?
a) Boron
b) Borax
c) Boroline
d) Borazole
View Answer
Explanation: Borazole, borazine and inorganic benzene are same and their chemical formula is given by B3N3H6, it is a colourless liquid having a six-membered ring of alternating Boron and nitrogen atoms (the reason why it’s called inorganic benzene).
12. In order to prepare borazine, we need by diborane and Ammonia in the ratio ____________
a) 5:9
b) 1:2
c) 22:23
d) 3:4
View Answer
Explanation: Borazine is prepared from diborane. When 3 moles of diborane combines with 6 moles of ammonia on heating, it gives two moles of inorganic benzene and 12 moles of hydrogen molecules, that means we need diborane and Ammonia in the ratio 1:2.
13. Is inorganic benzene reactive than Benzene?
a) Yes
b) No
c) Maybe
d) Cannot say
View Answer
Explanation: Yes, inorganic benzene is more reactive than Benzene. The formula for inorganic benzene is given by B3N3H6 and it is otherwise known as borazine or borazole. The pair of electrons and borazine are only partially localized, therefore we can say that it is more reactive than Benzene.
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