The d- and f- Block Elements Test

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The d- and f- Block Elements Test - 71

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Weekly Quiz Competition

Question 1
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In which of the following pairs are both the ions coloured in aqueous solution?

A
$$Sc^{3+}, Co^{2+}$$

B
$$Ni^{2+}, Cu^{+}$$

C
$$Ni^{2+}, Ti^{3+}$$

D
$$Se^{3+}, Ti^{3+}$$

Solution

$$Ni_{28}=1s^22s^22p^63s^23p^63d^84s^2$$

$$Ni^{2+}=1s^22s^22p^63s^23p^63d^8$$

$$Ti_{22}=1s^22s^22p^63s^23p^63d^24s^2$$

$$Ti^{3+}=1s^22s^22p^63s^23p^63d^1$$

$$Ni^{2+}$$ and $$Ti^{3+}$$ ions are coloured ions in aqueous solution due to the presence of unpaired electrons $$d-$$ subshell.
Question 2
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Which of the following sulphides is yellow in colour?

A
$$CuS$$

B
$$CdS$$

C
$$ZnS$$

D
$$CoS$$

Solution

Alkali and alkaline earth metal sulphides are colourless.

Heavy metal sulphides are unusually deeply coloured.

Both $$CuS$$ and $$CoS$$ are black coloured, $$ZnS$$ is bluish white.

$$CdS$$ is yellow in colour.

Hence the correct option is $$(B)$$.
Question 3
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Directions For Questions

Most of the compounds of the transition metals are coloured in the solid or in solution states. The colour of the transition metal ions arises from the excitation of electrons from the $$d-orbitals$$ of lower energy to the $$d-orbitals$$ of higher energy. The energy required for $$d-d$$ electron excitation is available in the visible range. Transition metal ions have the tendency to absorb certain radiations from the visible region and exhibit the complementary colour.

The transition metal ions which have completely filled $$d-orbitals$$ are colourless as the excitation of electron or electrons is not possible within $$d-orbitals.$$ The transition metal ions which have completely empty $$d-orbitals$$ are also colourless. In certain oxysalts of transition elements like $$KMnO_{4},\ K_{2}Cr_{2}O_{7},$$ there are no unpaired electrons at the central atom but they are deep in colour. The colour of these compounds is due to charge transfer spectrum. For example, in $$MnO_{4}^{-},$$ an electron momentarily transferred from $$O$$ to the metal and thus oxygen changes from $$O^{2-}$$ to $$O^{-}$$ and manganese from $$Mn(+VII)$$ to $$Mn(+VI).$$

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Which is a coloured ion?

A
$$[Cr(H_2O)_6]^{3+}$$

B
$$[Cu(CN)_4]^{3-}$$

C
$$[Ti(H_2O)_6]^{4+}$$

D
$$[Sc(H_2O)_6]^{3+}$$

Solution
Question 4
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Directions For Questions

Most of the compounds of the transition metals are coloured in the solid or in solution states. The colour of the transition metal ions arises from the excitation of electrons from the $$d-orbitals$$ of lower energy to the $$d-orbitals$$ of higher energy. The energy required for $$d-d$$ electron excitation is available in the visible range. Transition metal ions have the tendency to absorb certain radiations from the visible region and exhibit the complementary colour.

The transition metal ions which have completely filled $$d-orbitals$$ are colourless as the excitation of electron or electrons is not possible within $$d-orbitals.$$ The transition metal ions which have completely empty $$d-orbitals$$ are also colourless. In certain oxysalts of transition elements like $$KMnO_{4},\ K_{2}Cr_{2}O_{7},$$ there are no unpaired electrons at the central atom but they are deep in colour. The colour of these compounds is due to charge transfer spectrum. For example, in $$MnO_{4}^{-},$$ an electron momentarily transferred from $$O$$ to the metal and thus oxygen changes from $$O^{2-}$$ to $$O^{-}$$ and manganese from $$Mn(+VII)$$ to $$Mn(+VI).$$

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Which of the following compounds is (are) coloured due to charge transfer spectra and not due to $$d-d$$ transition?

A
$$KMnO_4$$

B
$$K_2CrO_4$$

C
$$CrO_3$$

D
All of these

Solution
Question 5
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On heating chromite $$(FeCr_2O_4)$$ with $$Na_2CO_3$$ in air, the following product is obtained:

A
$$Na_2CrO_4$$

B
$$Na_2Cr_2O_7$$

C
$$FeO$$

D
$$Fe_3O_4$$

Solution
Question 6
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Number of moles of $$K_2Cr_2O_7$$ radius by $$1$$ mole of $$Sn^{2+}$$ is:

A
$$1/6$$

B
$$2/3$$

C
$$1/3$$

D
$$1$$

Solution

The balanced chemical reactions (ionic reactions) for reduction of $$K_2Cr_2O_7$$ by $$Sn^{2+}$$ are;

$$Cr_2O_7^{2-}+14H^++6e^-\rightarrow 2Cr^{3+}+7H_2O$$

$$3(Sn^{2+}\rightarrow Sn^{4+}+2e^-)$$

Balances net equation: $$3Sn^{2+}+Cr_2O_7^{2-}+14H^+\rightarrow 3Sn^{4+}+2Cr^{3+}+7H_2O$$

Thus,

According to the balanced reaction, $$1$$ mole of $$Cr_2O_7^{2-}$$ will be reduced by $$3$$ moles of $$Sn^{2+}$$

Thus, $$1$$ mole of $$Sn^{2+}$$ will be reduced $$=\dfrac 13$$ moles of $$Cr_2O_7^{2-}$$

Hence the correct answer is option C.
Question 7
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Directions For Questions

Most of the compounds of the transition metals are coloured in the solid or in solution states. The colour of the transition metal ions arises from the excitation of electrons from the $$d-orbitals$$ of lower energy to the $$d-orbitals$$ of higher energy. The energy required for $$d-d$$ electron excitation is available in the visible range. Transition metal ions have the tendency to absorb certain radiations from the visible region and exhibit the complementary colour.

The transition metal ions which have completely filled $$d-orbitals$$ are colourless as the excitation of electron or electrons is not possible within $$d-orbitals.$$ The transition metal ions which have completely empty $$d-orbitals$$ are also colourless. In certain oxysalts of transition elements like $$KMnO_{4},\ K_{2}Cr_{2}O_{7},$$ there are no unpaired electrons at the central atom but they are deep in colour. The colour of these compounds is due to charge transfer spectrum. For example, in $$MnO_{4}^{-},$$ an electron momentarily transferred from $$O$$ to the metal and thus oxygen changes from $$O^{2-}$$ to $$O^{-}$$ and manganese from $$Mn(+VII)$$ to $$Mn(+VI).$$

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Select the correct statement:

A
Colour of the transition metal ion arises due to $$d-d$$ transition

B
Colour certain oxysalts of transition metals is due to charge transfer

C
Both are correct

D
None is correct

Solution
Question 8
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Which of the following sulphides is yellow?

A
$$ZnS$$

B
$$CdS$$

C
$$NiS$$

D
$$PbS$$

Solution

$$ZnS\rightarrow{White}$$

$$CdS\rightarrow{Yellow}$$ {Option (B) is correct.}

$$NiS\rightarrow{Brown}$$

$$PbS\rightarrow{Black}$$
Question 9
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Directions For Questions

Two types of magnetic behaviour are found in substances :
(a) Diamagnetism and (b) Paramagnetism

Diamagnetic substances are those which are repelled by an applied magnetic field. Such substances have no unpaired electron. Paramagnetic substances are those which are attracted by an applied magnetic field. Transition metals and many of their compounds show paramagnetic behaviour where there are unpaired electron or electrons. The magnetic moment arise from the spin and orbital motions in ions or molecules. Magnetic moment of $$n$$ unpaired electrons is given as,

$$\mu =\sqrt { n\left( n+2 \right) } $$ Bohr Magneton

Magnetic moment increases as the number of unpaired electrons increases.

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Which among the following ions has maximum value of magnetic moment?

A
$$Cu^{2+}$$

B
$$Mn^{2+}$$

C
$$Cr^{2+}$$

D
$$Ti^{2+}$$

Solution
Question 10
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Directions For Questions

(I)A powdered substance (A) on treatment with fusion mixture $$(K_{2}CO_{3}andKNO_{3})$$ gives a green coloured compound (B) (II) The solution of (B) in boiling water in acidification with dilute $$H_{2}SO_{4}$$ gives a pink coloured compound (C) (III) The aqueous solution of (A) on treatment with NaOH and $$Br_{2}$$ water gives a compound (D) (IV) A Solution of (D) in conc $$HNO_{3}$$ on treatment with lead peroxide at boiling temperature produced a compound (E) which was of the same colour at that of (C) (V) A solution of (A) on treatment with a solution of barium chloride gave white precipitate of compound (F) which was insoluble in conc . $$HNO_{3}$$ and conc HCl.

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Which of the following statements is correct ? (I) Anions of both (B) and (C) are diamagnetic and have tetrahedral geometry (II) Anions of both (B) and (C) are paramagnetic and have tetrahedral geometry (III) Anions of (B) is paramagnetic and that of (C) is diamagnetic but both have tetrahedral geometries (IV) Green coloured compound (B) in a neutral or acidic medium disproportionates to give (C) and (D)

A
I and II only

B
II and III only

C
II and IV only

D
III and IV only

Solution