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Chemistry NEET Questions — Free MCQ Practice

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${FeCr}_{2} O_{4} + 4 {Na}_{2} {CO}_{3} + O_{2} \overset{Fusion}{\to} [X] \to_{H_{2} O}^{H^{+}} [Y] \to_{H_{2} O_{2}}^{H^{+}} [Z]$

Which of the following statements is true for the compounds [X], [Y] and [Z] ?

A.

In all three compounds, the chromium is in +6 oxidation states.

B.

[Z] is a deep blue-violet coloured compound which decomposes rapidly in aqueous solution into

${Cr}^{3 +}$ and dioxygen.

C.

Saturated solution of [Y] gives a bright orange compound, chromic anhydride, with concentrated

$H_{2} {SO}_{4} .$

D.

All of these

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Explanation

(D)

$4 {FeCr}_{2} O_{4} + 8 {Na}_{2} {CO}_{3} + 7 O_{2} \overset{Fusion}{\to} {Na}_{2} \overset{+ VI}{Cr} O_{4} \to_{H_{2} O}^{H^{+}} {Na}_{2} \overset{+ VI}{{Cr}_{2}} O_{7} \overset{H^{+} / H_{2} O_{2}}{\to} \overset{+ VI}{Cr} O {(O_{2})}_{2} (deep blue violet) \overset{H_{2} O}{\to} O_{2} + H_{2} O + {Cr}^{3 +} .$

${Na}_{2} {Cr}_{2} O_{7} + H_{2} O_{4} \overset{}{\to} 2 {CrO}_{3} (chronic anhydride) + {Na}_{2} {SO}_{4} + H_{2} O .$

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${KMnO}_{4}$ on treatment with conc. $H_{2} {SO}_{4}$ forms a compound (X) which decomposes explosively on heating forming (Y). The (X) and (Y) are respectively :

A.

${Mn}_{2} O_{7}, {MnO}_{2}$

B.

${Mn}_{2} O_{7}, {Mn}_{2} O_{3}$

C.

${MnSO}_{4}, {MnO}_{2}$

D.

${Mn}_{2} {O_{3}}^{-}, {MnO}_{4}^{2 -}$

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Explanation

(A)

$2 {KMnO}_{4} + 3 H_{2} {SO}_{4} \overset{}{\to} 2 {KHSO}_{4} + {({MnO}_{3})}_{2} {SO}_{4} + 2 H_{2} O$

${({MnO}_{3})}_{2} {SO}_{4} + H_{2} O \overset{}{\to} {Mn}_{2} O_{7} + H_{2} {SO}_{4}$

${Mn}_{2} O_{7} \overset{∆}{\to} 2 {MnO}_{2} + 3 O_{2}$

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Assertion : The number of unpaired electrons in the following gaseous ions:

${Mn}^{3 +}, {Cr}^{3 +}, V^{3 +} and {Ti}^{3 +}$ are 4, 3, 2 and 1 respectively

Reason : ${Cr}^{3 +}$ is stable in aqueous solution.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

(B) ${Mn}^{3 +} = {[Ar]}^{18} 3 d^{4}, {Cr}^{3 +} = {[Ar]}^{18} 3 d^{3}, V^{3 +} = {[Ar]}^{18} 3 d^{2}, {Ti}^{3 +} = {[Ar]}^{18} 3 d^{1} and {Cr}^{3 +}$ is most

stable due to greater CFSE of $t_{2 g}^{3}$ configuration.

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Assertion : Cuprous ion $({Cu}^{+})$ is colourless whereas cupric ion $({Cu}^{2 +})$ produces blue colour in solution.

Reason : Cuprous ion $({Cu}^{+})$ has unpaired electrons while cupric ion $({Cu}^{2 +})$ does not.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

(C) Cupric ion produces blue colour in solution due to the presence of unpaired electron (d-d transition)

while cuprous ion does not have unpaired electron.

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Assertion : Ammonical silver nitrate converts glucose to gluconic acid and metallic silver is precipitated.

Reason : Glucose acts as a weak reducing agent.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

(A) ${Ag}_{2} O + C_{6} H_{12} O_{6} \overset{}{\to} 2 Ag + C_{6} H_{12} O_{7}$

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Assertion : To a solution of potassium chromate if a strong acid is added it changes its colour from

yellow to orange.

Reason : The colour change is due to the oxidation of potassium chromate.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

$(C) 2 \overset{+ 6}{Cr} O_{4}^{2 -} + 2 H^{+} \overset{+ 6}{{Cr}_{2}} O_{7}^{2 -} + H_{2} O (yellow) (orange)$

There is no change in oxidation state. So the explanation is wrong.

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Which one of the following statements is not correct

A.

Nickel forms Ni(CO)₄

B.

All the transition metals form mono metallic carbonyls

C.

Carbonyl are formed by transition metals

D.

Transition metals form complexes

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Explanation

Always transition metals combines with more than one carbonyl group.

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Which of the following pairs of compounds are more stable

A.

$K_{2} [N i C l_{6}], [P t (C N)_{4}]^{2 -}$

B.

NiCl₄, PtCl₄

C.

$[N i (C N)_{4}]^{2 -}, K_{2} [P t (C l_{6})]$

D.

PtCl₂, NiCl₂

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Explanation

By comparing the value of ionization energies the thermodynamic stability of transition metal compound can be compared. Ionization value shows that Ni(II) compound are more stable than Pt(II) compund while Pt(IV) compound are relatively more stable than Ni(IV).

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The radius of La³⁺ (atomic number of La=57) is 1.06 $\overset{o}{A}$ . Which one of the following given values will be closest to the radius of Lu³⁺ (atomic number of Lu =71)

A.

1.60 $\overset{o}{A}$

B.

1.40 $\overset{o}{A}$

C.

1.96 $\overset{o}{A}$

D.

0.85 $\overset{o}{A}$

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Explanation

The ionic radius of Lu³⁺ is 0.87 $\overset{o}{A}$ , which is very close to the value 0.85 $\overset{o}{A}$ .This decrease in the ionic radius is due to lanthanoid contraction.

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By calculating E^o value of the following reaction,which one of the following reaction are spontaneous.

Given

$E_{C u^{2 +} / C u}^{o} = 0.34 V, E_{Z n^{2 +} / Z n}^{o} = - 0.76 V, E_{A g^{+} / A g}^{o} = 0.80 V . (a) 2 A g + Z n^{2 +} \to 2 A g^{+} + Z n (b) C u + Z n^{2 +} \to Z n + C u^{2 +} (c) Z n + C u^{2 +} \to Z n^{2 +} + C u (d) 2 A g^{+} + C u \to 2 A g + C u^{2 +}$

A.

Only d

B.

Only b

C.

Both c & d

D.

Both a & c

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Chemistry MCQs for NEET — Practice Questions with Answers

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