This set of Class 11 Chemistry Chapter 11 Multiple Choice Questions & Answers (MCQs) focuses on “p-Block Elements – Important Trends and Anomalous Properties of Boron”.
1. Group 13 hydrides are formed directly.
Explanation: Elements of group 13 do not combine directly with hydrogen to form hydrides, therefore their hydrides have been prepared by indirect methods. An example is that diborane is formed when Boron fluoride is combined with lithium aluminium hydride in the presence of dry Ether.
2. All the oxides and hydroxides of Boron family are ____________ in nature.
c) acidic and basic
d) acidic, basic and amphoteric
Explanation: On moving top to bottom of the group, there is a change from acidic to amphoteric and then to basic character, of oxides and hydroxides of group 13 elements. Only boric acid is soluble in water while the other hydroxides are insoluble in water.
3. Which of the following is a colourless gas?
a) Boron chloride
b) Boron fluoride
c) Boron Bromide
d) Boron iodide
Explanation: All the halides of Boron are trihalides, boron chloride is a colourless fuming liquid, boron fluoride is a colourless gas, boron bromide is a colourless fuming liquid and Boron iodide is a white solid at room temperature, all these trihalides of boron are lewis acids.
4. Which of the following is true regarding the acidic character?
a) Aluminium halides acidic character is greater than that of indium halide
b) Boron halide acidic character is less than that of gallium halide
c) Gallium halides acidic character is less than that of indium halide
d) Aluminium halides acidic character is greater than that of boron halide
Explanation: The halides of group 13 elements behave as lewis acids. The correct order of their acidic character decreases from boron, aluminium, gallium and indium. Here halide refers to chlorine, bromine and iodine whereas thallium trichloride can act only as an oxidising agent as it decomposes easily.
5. Which of the following compound is formed when aluminium reacts with an alkali?
a) sodium Tetra hydroxyl aluminate V
b) sodium Tetra hydroxyl aluminate III
c) sodium Penta hydroxyl aluminate IV
d) sodium Septa hydroxyl aluminate III
Explanation: When two moles of aluminium atom is combined with two moles of sodium hydroxide in presence of 6 moles of water, two moles of sodium tetra hydroxyl aluminate III is formed along with three moles of the hydrogen molecule.
6. Which of the following element has the highest melting point?
Explanation: Boron has a very high melting point when compared to the other elements in group 13, this is because of its three-dimensional structure in which boron atoms are held together by strong covalent bonds, it also has a higher boiling point comparatively.
7. ____________ and Boron are same in case when reacted with concentrated nitric acid.
d) No other metal
Explanation: Boron can be oxidized by concentrated nitric acid, while aluminium becomes passive due to the formation of an oxide layer on the surface. Boron combines with nitric acid in order to produce boric acid and nitrous oxide.
8. Which of the following is the correct reason for the anomalous behaviour of Boron?
a) low ionization energy
b) smallest size in the group
c) low electronegativity
d) the presence of the orbital and can show allotropy
Explanation: Boron shows anomalous behaviour with the other members of the group because of the smallest size and the group, highest ionization energy, highest electronegativity in the group, absence of vacant d- orbital and the allotropy, while the other members do not show.
9. Boron shows a diagonal relationship with ____________
Explanation: There is a diagonal relationship between boron of group 13 and silicon of group 14 as they resemble each other like Lithium of group 1 and magnesium of group 2. There are many characteristics which resemble both boron and silicon.
10. Do Boron and silicon react with electropositive metals?
d) May not be
Explanation: Both boron and silicon form covalent hydrides like boranes and silanes respectively. They do react with electropositive metals and give binary compounds, which yield a mixture of boranes and silanes on hydrolysis.
11. Which of the following property is not a similarity between Boron and silicon?
b) non-metals metals
d) formation of covalent hydrides
Explanation: Boron of group 13 and silicon of group 14 share a diagonal relationship and have many similarities. Both boron and silicon are non-metals, semiconductors and they also form covalent hydrides, therefore, they are not metals.
12. Boron and silicon form covalent and volatile halides.
Explanation: Both boron of group 13 and silicon of group 14 form covalent and volatile halides, which fume in moisture air due to the release of HCl gas. They react with water in order to form boric acid and silicon hydroxide along with hydrochloric gas which is volatile in nature.
13. ____________ Boron is reactive with air.
a) Neither crystalline nor amorphous
c) Both crystalline and amorphous
Explanation: Crystalline Boron is unreactive whereas amorphous Boron is reactive. It reacts with air at 700-degree centigrade, boron combines with oxygen and nitrogen separately to form its oxide and nitride.
14. Which of the following elements do you think can react with water?
Explanation: Both boron and aluminium do not react with water but amalgamated aluminium reacts with water and evolves hydrogen. Gallium and indium do not react with cold or hot water but thallium forms an oxide layer on the surface.
15. Which of the following elements is more reactive with air?
d) all three are equally reactive
Explanation: Thallium is more reactive with their than gallium and indium, due to the formation of unipositive ion Tl+. Thallium combines with oxygen in the air in order to form thallium oxide, Tl2O is more stable than Tl2O3 due to inert pair effect.
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