p-Block Elements Test

Result

p-Block Elements Test - 9

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Weekly Quiz Competition

Question 1
1 / -0

Consider the following statements regarding the B-F bond in BF₃.

(A) The strength and bond length of BF₃ may be explained on the basis of pπ-pπ interactions between boron and fluorine.
(B) BF₃ is highly soluble in water.
(C) All the three B-F bond lengths are equal and less than the sum of the covalent radii of boron and fluorine.
(D) The bond order of the B-F is 1.33.

The correct order of initials T (true) and F (false) for the above statements is

A
T, T, T, T

B
F, T, T, F

C
T, T, F, F

D
T, F, T, T

Solution

All the statements are true.

Due to the pπ-pπ back bonding, the bond length decreases and is shorter than the sum of the covalent radii of boron and fluorine. As a consequence, the bond strength increases.

BF₃ can be represented by 3 resonating structures and hence, the three B-F bonds are alike and the bond order is 1.33.

BF₃ is soluble in water because it forms hydrates such as BF₃.H₂O and BF₃.2H₂O.
Question 2
1 / -0

Consider the following statements about borax:

(a) It is used as a flux for soldering.
(b) It is used in making enamels and pottery glaze.
(c) It is used as a styptic to stop bleeding.
(d) It is used for making optical glasses.

Which of the following is not the use of borax?

A
Only (a)

B
Only (b)

C
Only (c)

D
Only (d)

Solution

Borax is not used as a styptic to stop bleeding. Rest are the uses of borax.
Question 3
1 / -0

Alum helps in purifying water by

A
forming a soluble complex with the clay particles

B
the combination of the sulphate part with the dirt to finally remove it

C
coagulating the mud particles

D
making muddy particles water soluble

Solution

Potassh alum is K₂SO₄.Al₂(SO₄)₃.24H₂O.
Muddy water is a lyophobic colloid with negatively charged colloidal particles. Alum is an electrolyte and the cations neutralise the charge on the colloidal particles causing them to coagulate together.
Therefore, alum is added to impure water to coagulate the suspended impurities and make water fit for drinking purpose.
Question 4
1 / -0

Which of the following statements are correct?

(A) Diborane is a coloured gas and stable at low temperature.
(B) The members of B_nH_n+6series are less stable than those of B_nH_n+4series.
(C) The reaction of diborane with oxygen is endothermic in nature.
(D) It has banana bonds.

A
A, B and C

B
B, C and D

C
A, C and D

D
B and D

Solution

Diborane is a colourless gas and unstable. Hence, (A) is incorrect.

The members of B_nH_n+6 series are less stable than those of B_nH_n+4 series because +3 is a more stable oxidation state of boron than +4. Hence, (B) is correct.

B₂H₆ + 3O₂ → B₂O₃ + 3H₂O; ΔH is negative. Hence, (C) is incorrect.
Question 5
1 / -0

A solid element 'X' is a good conductor of electricity and forms two chlorides - XCl_n (a colourless volatile liquid) and XCl_{n - 2} (a colourless solid). To which group of periodic table does the element 'X' belong?

A
Group 13

B
Group 14

C
Group 15

D
Group 16

Solution

The element 'X' belongs to Group 14 as the common oxidation states of Group 14 elements are +2 and +4.
The element is Pb.
PbCl₄ is a colourless, oily and volatile liquid, whereas, PbCl₂ is a white powder.