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NEET NEET Questions — Free MCQ Practice

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Which one of the following statements is correct when SO₂ is passed through acidified K₂Cr₂O₇ solution?

A.

The solution is decolourized

B.

SO₂ is reduced

C.

Green Cr₂(SO₄)₃ is formed

D.

The solution turns blue

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Explanation

(C) When SO₂ is passed through acidified K₂Cr₂O₇ solution, green chromium sulphate is formed. In this reaction, oxidation state of Cr changes from +6 to +3.

K₂Cr₂O₇ + H₂SO₄ + 3SO_{2 $\to$}K₂SO₄ + Cr₂(SO₄)₃ + H₂O

The appearance of green colour is due to the reduction of chromium metal.

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Because of lanthanoid contraction, which of the following pairs of elements have nearly same atomic radii? (Numbers in the parenthesis are atomic numbers).

A.

Ti (22) and Zr (40)

B.

Zr (40) and Nb (41)

C.

Zr (40) and Hf (72)

D.

Zr (40) and Ta (73)

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Explanation

Because of the lanthanoid contraction Zr (atomic radii 160 pm) and Hf (atomic radii 158 pm) have nearly same atomic radii.

Lanthanoids include the elements from lanthanum La (Z = 57) to lutetium Lu(Z = 71). zirconium Zr(40) belong to the second transition series (4d) and Hf (72) belongs to third transition series (5d). Lanthanoid contraction is associated with the intervention of the 4f orbitals which are filled before the 5d-series of elements starts. The filling of 4f if orbitals before 5d-orbitals results in regular decrease in atomic radii which compensates the expected increase in atomic size with increasing atomic number. As a result of this lanthanoid contraction, the elements of second and third transition series have almost similar atomic radii.

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Which of the following processes does not involve oxidation of iron?

A.

Rusting of iron sheets

B.

Decolourisation of blue CuSO₄ solution by iron

C.

Formation of Fe(CO)₅ from Fe

D.

Liberation of H₂ from steam by iron a high temperature

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Explanation

0 III

(a) Fe +H₂O+O₂→Fe₂O₃. x [H₂O]
(From air)

0 II
(b) Fe+CuSO₄→FeSO₄+Cu

0 0
(c) Fe+5CO_^→Fe(CO₅)

0 III
(d) Fe+H₂O→Fe₂O₃+H₂

∴ Formation of Fe(CO)₅ from Fe does not involve oxidation of iron because there 18 no change in oxidation state.

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Gadolinium belongs to 4f series. It's atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?

A.

[Xe]4f⁸6d²

B.

[Xe]4f⁹5s¹

C.

[Xe]4f⁷5d¹6s²

D.

[Xe]4f⁶5d²6s²

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Explanation

(c) ₆₄Gd = [Xe]4f⁷5d¹6s²

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Assuming complete ionisation, same moles of which of the following compounds will require the least amount of acidified KMnO₄ for complete oxidation?

A.

FeSO₄

B.

FeSO₃

C.

FeC₂O₄

D.

Fe(NO₂)₂

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Explanation

FeSO₄ will require the least amount of acidified KMnO₄ for complete oxidation.

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Reason of lanthanoid contraction is

A.

negligible screening effect of 'f orbitals

B.

increasing nuclear charge

C.

decreasing nuclear charge

D.

decreasing screening effect

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Explanation

(a) Lanthanoid contraction is the regular decrease in atomic and ionic radii of lanthanides. This is due to the imperfect shielding or poor screening effect of orbitals due to their diffused shape, which unable to counterbalance the effect of the increased nuclear charge. Hence, the net result is a contraction in size of lanthanoids.

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KMnO₄ can be prepared from K₂MnO₄ as per reaction

$3 {MnO}_{4}^{2 -} + 2 H_{2} O ⇌ 2 {MnO}_{4}^{-} + {MnO}_{2} + 4 {OH}^{-}$

The reaction can go to completion by removing OH^- ions by adding

A.

HCl

B.

KOH

C.

CO₂

D.

SO₂

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Explanation

Since OH^- are generated from weak acid (H₂O), a weak acid (like CO₂) should be used to remove it because of strong acid (HCl) reverse the reaction. KOH increases the concentration of OH^-, thus again shifts the reaction in backward side. CO₂ combines with OH^- to give carbonate which is easily removed. SO₂ reacts with water to give strong acid, so it cannot be used.

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Which of the following statements about the interstitial compounds is incorrect ?

A.

They retain metallic conductivity

B.

They are chemically reactive

C.

They are much harder than the pure metal

D.

They have higher melting points than the pure metal

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Explanation

(b) Interstitial compounds are obtained when small atoms like H, B, C. N etc., fit into the lattice of other elements. These retain metallic conductivity. These resemble the parent metal in chemical properties (reactivity) but differ in physical properties like hardness, melting point etc.But they are chemically inactive

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Identify the alloy containing a non-metal as a constituent in it.

A.

lnvar

B.

Steel

C.

Bell metal

D.

Bronze

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Explanation

Alloy	Constituents
Invar	Fe+Ni
Steel	Fe+C
Bell Metal	Cu (80%)+Sn (20%)
Bronze	Cu (75.90%)+Sn (10.25%)

Among these alloys only steel contains carbon, which is a non-metal.

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For the four successive transition elements (Cr, Mn, Fe and Co), the stability of +2 oxidation state will be there in which of the following order? (At. no. Cr=24;Mn=25&Fe=26,Co=27)

A.

Fe>Mn>Co>Cr

B.

Co>Mn>Fe>Cr

C.

Cr>Mn>Co>Fe

D.

Mn>Cr>Fe>Co

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Explanation

This can be understood on the basis of E° values for M²⁺/M.

E°/V Cr Mn Fe Co
M²⁺/M -0.90 -1.18 -0.44 -0.28

E° value for Mn is more negative than expected from general trend due to extra stability of half-filled Mn²⁺ ion.

Thus,the correct order should be:-
Mn>Cr>Fe>Co

An examination of E° values for redox couple M³⁺/ M²⁺ shows that Cr²⁺ is strong reducing
agent (E° M³⁺/M²⁺=0.41V) and liberates H₂ from dilute acids.

2Cr²⁺ (aq) + 2H⁺ (aq)→ 2Cr³⁺(aq) + H₂↑(g)

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