p-Block Elements

JEE Chemistry · 225 questions · Page 16 of 23 · Click an option or "Show Solution" to reveal answer

Q151

The number of P−OH bonds and the oxidation state of phosphorus atom in pyrophosphoric acid (H4P2O7) respectively are :

A four and four

B five and four

C five and five

D four and five

Correct Answer

Option D

Solution

Number of P - OH bonds = 4 Let the oxidation number of P = x $\therefore$ In H4 P2 O7 for 7 oxygen = 7 $\times$ ( $-$ 2) = $-$ 14 for 4 Hydrogen = 4 $\times$ (+1) = 4 For 2 Phosphorus = 2x $\therefore$ 2x + 4 $-$ 14 = 0 $\Rightarrow$ x = + 5

Q152

The number of bonds between sulphur and oxygen atoms in S2O82- and the number of bonds between sulphur and sulphur atoms in rhombic sulphur, respectively, are :

A 4 and 8

B 8 and 6

C 4 and 6

D 8 and 8

Correct Answer

Option D

Solution

number of bond between sulphur and oxygen = 8 number of bond between sulphur and sulphur = 8

Q153

Dinitrogen is a robust compound, but reacts at high altitudes to form oxides. The oxide of nitrogen that can damage plant leaves and retard photosynthesis is :

\mathrm{NO}

\mathrm{NO}_{3}^{-}

\mathrm{NO}_{2}

\mathrm{NO}_{2}^{-}

Correct Answer

Option C

Solution

High concentration of NO2 can damage plant leaves and retard photosynthesis.

Q154

Element not showing variable oxidation state is :

A Bromine

B Iodine

C Chlorine

D Fluorine

Correct Answer

Option D

Solution

Fluorine is the element among the options that does not exhibit a variable oxidation state, unlike its fellow halogens.

This is because fluorine is the most electronegative element, and it always forms compounds in the oxidation state of -1 as it has a strong tendency to gain one electron to achieve a stable electronic configuration.

Q155

The compound that does not produce nitrogen gas by the thermal decomposition is :

A (NH4)2SO4

B Ba(N3)2

C (NH4)2Cr2O7

D NH4NO2

Correct Answer

Option A

Solution

Thermal decomposition reaction of the given compounds are . . . (NH4)2SO4

\overset{\Delta}\longrightarrow

2 NH3(g) + H2SO4 Ba (N3)2

\overset{\Delta}\longrightarrow

Ba + 3N2(g) NH4NO2

\overset{\Delta}\longrightarrow

N2(g) + 2H2O (NH4)2Cr2O7

\overset{\Delta}\longrightarrow

N2(g) + 4H2O + Cr2O3 So, here you can see only (NH4)2SO4 does not give N2 by thermal decomposition it gives NH3 while other give N2 gas

Q156

On heating, lead (II) nitrate gives a brown gas (A). The gas (A) on cooling changes to a colourless solid/liquid (B). (B) on heating with NO changes to a blue solid (C). The oxidation number of nitrogen in solid (C) is :

A +3

B +4

C +5

D +2

Correct Answer

Option A

Solution

Pb(NO3 )2 $\to$ PbO + NO2[(A) Brown gas] + O2 2NO2

\overset{{cooling}}\longrightarrow

N2O4[(C) colourless solid] N2O4 + NO

\overset{\Delta}\longrightarrow

N2O3 [(C) Blue Solid] Let oxidation state of N in N2O3 is x. $\therefore$ 2x + 3 (–2) = 0 $\Rightarrow$ x = +3

Q157

Graphite is a soft solid lubricant extremely difficult to melt. The reason for this anomalous behaviour is that graphite :

A is an allotropic form of diamond

B has molecules of variable molecular masses like polymers

C has carbon atoms arranged in large plates of rings of strongly bound carbon atoms with weak interplate bonds

D is a non-crystalline substance

Correct Answer

Option C

Solution

In graphite, carbon is

s{p^2}

hybridized.

Each carbon is thus linked to three other carbon atoms forming hexagonal rings.

Since only three electrons of each carbon are used in making hexagonal ring, fourth electron of each carbon is free to move.

This makes graphite a good conductors of heat and electricity.

Further graphite has a two dimensional sheet like structure.

These various sheets are held together by weak van der Waal's force of attraction. due to these weak forces of attraction, one layer can slip over the other.

This makes graphite soft and a good lubricating agent.

Q158

Boron and silicon of very high purity can be obtained through :

A Liquation

B Electrolytic refining

C Zone refining

D Vapour phase refining

Correct Answer

Option C

Solution

For boron and silicon zone refining is used.

Q159

The number of hydrogen atom(s) attached to phosphorus atom in hypophosphorous acid is :

A zero

B two

C one

D three

Correct Answer

Option B

Solution

Two

H

-atoms are attached to

P

atom.

Q160

Which of the following statements regarding sulphur is incorrect?

A The vapour at 200oC consists mostly of S8 rings

B At 600oC the gas mainly consists of S2 molecules

C The oxidation state of sulphur is never less than +4 in its compounds

D S2 molecule is paramagnetic.

Correct Answer

Option C

Solution

Oxidation of sulphur varies from

-2

+6

in its various compounds.

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