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Chemistry NEET Questions — Free MCQ Practice

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Mark the incorrect statement:

A.

Alkali metals are strong reducing agents.

B.

The electropositive nature of alkali metals decreases with increase in atomic number.

C.

Alkali metals have relatively low electronegativity values.

D.

On burning in oxygen lithium forms only the monoxide while other alkali metals form peroxides and or superoxides.

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Explanation

(B). Since ionisation energy decreases on moving down the group, the electropositive character increases on moving down from lithium towards cesium.

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A hydrated water soluble salt, A in solution gives a turbidity with dilute hydrochloric acid evolving a gas with a suffocation odour. The solution of A decolourises lodine solution. A is likely to be

A.

KI

B.

$N a_{2} S O_{4} . 10 H_{2} O$

C.

$N a_{2} S_{2} O_{3} . 5 H_{2} O$

D.

$A g N O_{3}$

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Explanation

(C). The reactions are

$N a_{2} S_{2} O_{3} + 2 H C l \to 2 N a C l + S O_{2} ↑ + S ↓ + H_{2} O$

$2 N a_{2} S_{2} O_{3} + I_{2} \to 2 N a I + \underset{(S o d i u m t e t r a t h i o n a t e)}{N a_{2} S_{4} O_{6}}$

Sodium thiosulfate is an inorganic compound with the formula Naâ‚‚Sâ‚‚Oâ‚ƒxHâ‚‚O. Typically it is available as the white or colorless pentahydrate, Naâ‚‚Sâ‚‚Oâ‚ƒ·5Hâ‚‚O. The solid is an efflorescent crystalline substance that dissolves well in water.

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Which of the following compounds may be soluble in pyridine-

A.

Barium chloride

B.

Sodium chloride

C.

Lithium chloride

D.

Potassium chloride

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Explanation

(C). Due to high positive charge density on $L i^{+}$ , it forms compounds with maximum covalent character. So lithium chloride may be soluble in pyridine.

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Which of the following statement regarding isolation of Na and K metal is true –

A.

These metals can be isolated by the reduction of their oxides

B.

These metals can be prepared from their aqueous salt solutions by metal displacement

C.

These metals can be prepared by the electrolysis of their aqueous salt solutions

D.

These metals can be prepared by the electrolysis of their fused chlorides

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Explanation

(D). Sodium and potassium can be prepared by the electrolysis of their fused chlorides but not from aqueous solutions of their salts, because these metals are very reactive.

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Which of the following is a false statement-

A.

Sodium oxide is more basic then magnesium oxide.

B.

Beryllium oxide is amphoteric

C.

The thermal stability of beryllium carbonate is more than that of calcium carbonate

D.

Beryllium is amphoteric

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Explanation

(C). The thermal stability of calcium carbonate is more as compared to that of beryllium carbonate. The ionic potential ( $ϕ$ ) value of $B e^{2 +}$ is more than that of $C a^{2 +}$ . So $B e^{2 +}$ attracts the oxygen of $C O_{3}^{2 -}$ more and on heating beryllium carbonate losses $C O_{2}$ more easily.

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The basic character of oxides MgO, SrO, $K_{2} O$ , NiO and $C s_{2} O$ increases in the order –

A.

$M g O > S r O > K_{2} O > N i O > C s_{2} O$

B.

$C s_{2} O > K_{2} O > M g O > S r O > N i O$

C.

$N i O < M g O < S r O < K_{2} O < C s_{2} O$

D.

$K_{2} O < N i O < M g O < S r O < C s_{2} O$

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Explanation

(C). Alkali metal oxides are more basic than alkaline earth metal oxides and basic nature increases as we move down the group.

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Assertion : s-block elements do not occur free in nature

Reason : s-block elements are highly electropositive in nature.

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). The s-block elements are highly electropositive in nature. So, these are very reactive. That is why these elements do not occur free in nature. Usually, the s-group elements occur in nature as halides, carbonates and sulphates. These metals are obtained from their molten halides by electrolytic reduction.

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Assertion : The alkaline earth metals have much higher melting and boiling points than those of the alkali metals.

Reason : The melting and boiling points of alkaline earth metal do not vary in a regular fashion.

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). Atom/ions of alkaline earth metals are smaller than the corresponding alkali metals. These atoms/ions are packed more closely in their lattices. Alkaline earth metals have two valence electrons and alkali metals have only one. Larger number of valence electrons leads to stronger interatomic interactions in alkaline earth metals. As a result, therefore, the melting and boiling points of alkaline earth metals are higher than those of alkali metals.

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Assertion : The ionisation enthalpies of alkaline earth metals are fairly low.

Reason : In general, the low ionisation enthalpies of alkaline earth metals are due to large size of their atoms.

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). Alkali metals have only one valence electron, while alkaline earth metals have two valence electrons. After the only outermost electron is removed from the atom of an alkali metal, the ion formed has a stable configuration of the nearest noble gas. Removal of another electron from the unipositive ion of alkali metal, therefore, would require very large amount of energy.

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Both Be and Al become passive on reaction with concentrated nitric acid due to:

A.

The non reactive nature of the metal.

B.

The non reactive nature of the acid.

C.

The formation of an inert oxide layer on the surface of the metals

D.

None of these.

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Explanation

Both Be and Al are rendered passive due to formation of inert, insoluble and impervious oxide layer on their surface.

Chemistry MCQs for NEET — Practice Questions with Answers

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