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The variation of the boiling point of the hydrogen halides is in the order HF > HI > HBr > HCl. What explains the higher boiling point of hydrogen fluoride?

The electronegativity of fluorine is much higher than for other elements in the group

There is strong hydrogen bonding between HF molecules

The bond energy ol HF molecules is greater than in other hydrogen halides

The effect of nuclear shielding is much reduced in fluorine which polarises the HF molecule

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Explanation

Since, there is a strong hydrogen bonding between HF molecules. Hence, boiling point is highest for HF.
HF > HI > HBr > HI

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Acidity of diprotic acids in aqueous solutions increases in the order:-

H₂S<H₂Se<H₂Te

H₂Se<H₂S<H₂Te

H₂Te<H₂S<H₂Se

H₂Se<H₂Te<H₂S

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Explanation

(a) Acidic strength of hydrides increases as the size of central atom increases which weakens the M-H bond. Since, the size increases from S to Te thus acidic strength follows the order

H₂S<H₂Se<H₂Te

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Roasting of sulphides gives the gas X as a by-product. This is a colourless gas with choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic acts as a reducing agent and its acid has never been isolated. The gas X is

H₂S

SO₂

CO₂

SO₃

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Explanation

(b) SO₂ gas is obtained when any sulphide ore is roasted.

2M₂S + 3O₂ $\to$ 2M₂O + 2SO₂

This gas exhibits all the characteristics given in the question.

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When Cl₂ gas reacts with hot and concentrated sodium hydroxide solution, the oxidation number of chlorine changes from

zero to +1 and zero to -5

zero to -1 and zero to +5

zero to -1 and zero to +3

zero to +1 and zero to -3

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Explanation

When Clâ‚‚ gas reacts with hot and concentrated NaOH solution, chlorine undergoes disproportionation. Its oxidation states change from 0 to -1 (in NaOCl) and 0 to +5 (in NaClOâ‚ƒ). This disproportionation reaction is used in the manufacturing of bleaching powder.

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The reaction of hydrogen and iodine monochloride is given as :

H₂(g)+ 2ICl(g) $\to$ 2HCl(g)+ I₂(g)

This reaction is of first order with respect to H₂(g) and 2ICl(g) following mechanisms were proposed:

Mechanism A:

H₂(g)+ 2ICl(g) $\to$ 2HCl(g)+ I₂(g)

Mechanism B :

H₂(g)+ ICl(g) $\to$ HCl(g)+ HI(g) ; slow

HI(g)+ ICl(g) $\to$ HClCg) + I2(g); fast

Which of the above mechanism (s) can be consistent with the given information about the reaction ?

B only

A and B both

Neither A nor B

A only

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Explanation

Rate of reaction is always depends on slow reaction.

H₂(g)+ 2ICl(g) $\to$ 2HCl(g)+ I₂(g) is first order reaction respect to H₂ and I₂ can be measured with the help of both mechanism A and B.

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In case of hydride of oxygen family, which of the following physical property change regularly on moving down the group.

Melting point

Thermal stability

Boiling point

Critical temperature

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Explanation

(b) Order of M.P. or B.P. or critical temperature : $H_{2} O > H_{2} Te > H_{2} Se > H_{2} S$

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In which case, the order of acidic strength is not correct ?

$HI > HBr > HCl$

${HIO}_{4} > {HBrO}_{4} > {HCIO}_{4}$

${HClO}_{4} > {HClO}_{3} > {HClO}_{2}$

$HF > H_{2} O > {NH}_{3}$

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Explanation

(b) ${HIO}_{4} > {HBrO}_{4} > {HCIO}_{4}$ $\Rightarrow$ acidic strength has been decided on the basis of

electronnegativity or charge density on central atom.

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Concentrated nitric acid reacts with iodine to give :

$HOI$

$HI$

${HIO}_{3}$

${HIO}_{4}$

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Explanation

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Which of the following has been arranged in order of decreasing bond dissociation energy :

$P — O > Cl — O > S — O$

$P — O > S — O > Cl — O$

$S — O > Cl — O > P — O$

$Cl — O > S — O > P — O$

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Explanation

(d) Bond dissociation energy $\propto \frac{1}{Bond length}$

Orders of bond length $P — O > S — O > Cl — O$ Order of $BDE :$ $Cl — O > S — O > P — O$

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Two oxides of nitrogen, $NO$ and ${NO}_{2}$ are allowed to react together at $243 ° K$ and form a coloured compound of nitrogen (X). When compound (X) reacts with water to yield another compound of nitrogen (Y). The shape of the anion of (Y) molecule is :

triangular planar

triangle pyramidal

tetrahedron

square planar

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