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Chemistry MCQs for NEET — Practice Questions with Answers

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Polyphosphates are used as water softening agents because they –

form soluble complexes with anionic species

precipitate anionic species

form soluble complexes with cationic species

precipitate cationic species

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Explanation

(C). Sodium hexametaphosphate $-$ a polyphosphate, combines with cations $(i . e ., {Ca}^{2 +}, {Mg}^{2 +})$ to

form soluble complexes.

$2 {Ca}^{2 +} + {Na}_{2} [{Na}_{4} {({PO}_{3})}_{6}] \to 4 {Na}^{+} + {Na}_{2} [{Ca}_{2} {({PO}_{3})}_{6}] complex (soluble)$

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$H_{2} O$ has higher boiling point than $H_{2} S$ because.

$H_{2} O$ is a smaller molecule and hence more closely packed

The bond angle in $H_{2} O$ is more than in $H_{2} S$ and hence the former molecules are more tightly packed

Of intermolecular hydrogen bonding in liquid $H_{2} O$

The latent heat of vaporisation is higher for $H_{2} O$ than for $H_{2} S$

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Explanation

(C). The b.p of $H_{2} O$ is higher than that of $H_{2} S$ because of intermolecular hydrogen bonding in

liquid $H_{2} O$ .

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The maximum possible number of hydrogen bonds a water molecule can form is –

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Explanation

(B). Water molecules can form two hydrogen bonds through its two hydrogen atoms and another

two with two lone pairs of electrons on the O atom.

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In which of the following reactions is $H_{2} O_{2}$ acting as an acid.

$2 {KMnO}_{4} + 3 H_{2} {SO}_{4} + 5 H_{2} O_{2} \to K_{2} {SO}_{4} + {MnO}_{4} + 2 {MnSO}_{4} + 8 H_{2} O + 5 O_{2}$

$2 K_{3} Fe {(CN)}_{6} + 2 KOH + H_{2} O_{2} \to 2 K_{4} Fe {(CN)}_{6} + 2 H_{2} O + O_{2}$

$O_{3} + H_{2} O_{2} \to H_{2} O + 2 O_{2}$

$Ba {(OH)}_{2} + H_{2} O_{2} \to {BaO}_{2} + H_{2} O_{2}$

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Explanation

(D). $Ba {(OH)}_{2} + H_{2} O_{2} \to {BaO}_{2} + 2 H_{2} O$ is similar to acid base (neutralisation reaction). Aqueous

solution of $H_{2} O_{2}$ is weakly acidic.

$H_{2} O_{2} + H_{2} O \to H_{3} O^{+} + {HO}_{2}^{-}$

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The best explanation for not placing hydrogen with the group of alkali metals or halogens is.

Hydrogen can form compounds with all other elements

Hydrogen is much lighter element than the alkali metals or the halogens

The IE of hydrogen is too high for group of alkali metals but too low for halogen group

None of these

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Explanation

(C). The IE of hydrogen is much higher than those of alkali metals and slightly higher than those

of halogens. For example IE of Cl is 1255 kJ/mole and IE of H is 1312 kJ/mole.

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A substance gives off $O_{2}$ when heated, turns an acid solution of $KI$ violet, and reduces acidified ${KMnO}_{4}$ . The substance is –

${SO}_{3}$

${KNO}_{3}$

$H_{2} O_{2}$

All of these

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Explanation

(C). These are the properties of $H_{2} O_{2}$ .

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Assertion : Beryllium hydride is a covalent hydride.

Reason : The electronegativity difference between $Be$ and $H$ is very high.

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). The electronegativity difference between $Be (1.5)$ and $H (2.1)$ is small.

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Assertion : The $O - O$ bond length of $H_{2} O_{2}$ is shorter than that of $O_{2} F_{2} .$

Reason : $H_{2} O_{2}$ is an ionic compound.

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Explanation

(D). The lone pairs of electrons on the O atoms are strongly attracted by the electronegative F

atoms. As a result, lone pair-lone pair repulsion of the two oxygen atoms is far less in $O_{2} F_{2}$

than in $H_{2} O_{2}$ . As a result, $O - O$ bond length is $O_{2} F_{2}$ (1.22 $\overset{\circ}{A}$ ) is much shorter than in

$H_{2} O_{2}$ (1.48 $\overset{\circ}{A}$ )

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Of the two solvents $H_{2} O a n d D_{2} O$ , NaCl dissolves:

equally in both

only in $H_{2} O$

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