# JEE Main

Explore popular questions from Some pBlock Elements for JEE Main. This collection covers Some pBlock Elements previous year JEE Main questions hand picked by experienced teachers.

# Mathematics

Some pBlock Elements

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Q 1. In {tex} \mathrm { XeF } _ { 2 } , \mathrm { XeF } _ { 4 } , \mathrm { XeF } _ { 6 } {/tex} the number of lone pairs on {tex} \mathrm { Xe } {/tex} are respectively

A

{tex} 2,\ 3, \ 1 {/tex}

B

{tex} 1,\ 2, \ 3 {/tex}

C

{tex} 4, \ 1, \ 2 {/tex}

{tex} 3, \ 2, \ 1 {/tex}.

##### Explanation

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Q 2. Glass is a

A

micro-crystalline solid

super-cooled liquid

C

gel

D

polymeric mixture.

##### Explanation

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Q 3. Graphite is a soft solid lubricant extremely difficult is to melt. The reason for this anomalous behaviour is that graphite

A

is a non-crystalline substance

B

is an allotropic form of diamond

C

has molecules of variable molecular masses like polymers

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

##### Explanation

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Q 4. Which one of the following processes doesn't produce hard water?

A

Saturation of water with {tex} \mathrm { CaCO } _ { 3 } {/tex}

B

Saturation of water with {tex} \mathrm { MgCO } _ { 3 } {/tex}

Addition of {tex} \mathrm { Na } _ { 2 } \mathrm { SO } _ { 4 } {/tex} to water

D

Saturation of water with {tex} \mathrm { CaSO } _ { 4 } {/tex}

##### Explanation

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Q 5. Which one of the following substances has the highest proton affinity?

A

{tex} \mathrm { H } _ { 2 } \mathrm { O } {/tex}

B

{tex} \mathrm { H } _ { 2 } \mathrm { S } {/tex}

{tex} \mathrm { NH } _ { 3 } {/tex}

D

{tex} \mathrm { PH } _ { 3 } {/tex}.

##### Explanation

As ammonia is strongest base among given compounds, so it has highest affinity for hydrogen ions.

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Q 6. Which one of the following is an amphoteric oxide?

{tex} \mathrm { ZnO } {/tex}

B

{tex} \mathrm { Na } _ { 2 } \mathrm { O } {/tex}

C

{tex} \mathrm { SO } _ { 2 } {/tex}

D

{tex}\mathrm B _ { 2 }\mathrm O _ { 3 } {/tex}.

##### Explanation

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Q 7. Concentrated hydrochloric acid when kept in open air sometimes produces a cloud of white fumes. The reason for that could be:

A

concentrated hydrochloric acid emits strongly smelling {tex}\mathrm{HCl}{/tex} gas all the time

B

oxygen in air reacts with the emitted {tex}\mathrm{HCl}{/tex} gas to form a cloud of chlorine gas

strong affinity of {tex}\mathrm{HCl}{/tex} gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke

D

due to strong affinity for water, concentrated hydrochloric acid pulls moisture of air towards itself. This moisture forms droplets of water and hence the cloud.

##### Explanation

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Q 8. The states of hybridisation of boron and oxygen atoms in boric acid {tex} \left( \mathrm { H_3 } \mathrm { BO } _ { 3 } \right) {/tex} are respectively

A

{tex} s p ^ { 2 } {/tex} and {tex} s p ^ { 2 } {/tex}

{tex} s p ^ { 2 } {/tex} and {tex} s p ^ { 3 } {/tex}

C

{tex} s p ^ { 3 } {/tex} and {tex} s p ^ { 2 } {/tex}

D

{tex} s p ^ { 3 } {/tex} and {tex} s p ^ { 3 } {/tex}.

##### Explanation

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Q 9. Which one of the following statements regarding helium is incorrect?

It is used to fill gas in balloons instead of hydrogen because it is lighter and non-inflammable.

B

It is used as a cryogenic agent for carrying out experiments at low temperatures.

C

It is used to produce and sustain powerful superconducting magnets.

D

It is used in gas-cooled nuclear reactors.

##### Explanation

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Q 10. The molecular shapes of {tex} \mathrm { SF } _ { \mathrm { 4 } } , \mathrm { CF } _ { 4 } {/tex} and {tex} \mathrm { XeF } _ { 4 } {/tex} are

A

the same with {tex} 2,0 {/tex} and {tex}\mathrm{1}{/tex} lone pairs of electrons on the central atom respectively.

B

the same with {tex} 1,1 {/tex} and {tex}\mathrm{1}{/tex} lone pair of electrons on the central atoms respectively.

C

different with {tex} 0,1 {/tex} and {tex}\mathrm{2}{/tex} lone pairs of electrons on the central atom respectively.

different with {tex} 1,0 {/tex} and {tex} 2 {/tex} lone pairs of electrons on the central atom respectively.

##### Explanation

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Q 11. The correct order of the thermal stability of hydrogen halides H-X {tex} ( \mathrm { H } - X ) {/tex} is

A

{tex} \mathrm { HI } > \mathrm { HBr } > \mathrm { HCl } > \mathrm { HF } {/tex}

{tex} \mathrm { HF } > \mathrm { HCl } > \mathrm { HBr } > \mathrm { HI } {/tex}

C

{tex} \mathrm { HCl } < \mathrm { HF } > \mathrm { HBr } < \mathrm { HI } {/tex}

D

{tex} \mathrm { HI } > \mathrm { HCl } < \mathrm { HF } > \mathrm { HBr } {/tex}

##### Explanation

As the size of the halogen atom increases from F to I, H – X bond length in HX molecules also increases from H – F to H – I (H – F < H – Cl < H – Br < H – I). The increase in H – X bond length decreases the strength of H – X bond from H – F to H – I (H – F > H – Cl > H – Br > H – I). The decrease in the strength of H – X bond is evident from the fact that H – X bond dissociation energies decrease from H – F to H – I. Due to successive decrease in the strength of H – X bond from H – F to H – I, thermal stability of HX molecules also decreases from HF to HI (HF > HCl > HBr > HI).

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Q 12. In silicon dioxide

each silicon atom is surrounded by four oxygen atoms and each oxygen atom is bonded to two silicon atoms

B

each silicon atom is surrounded by two oxygen atoms and each oxygen atom is bonded to two silicon atoms

C

silicon atom is bonded to two oxygen atoms

D

there are double bonds between silicon and oxygen atoms

##### Explanation

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Q 13. Which of the following statements is true?

A

{tex} \mathrm { H } _ { 3 } \mathrm { PO } _ { 3 } {/tex} is a stronger acid than {tex} \mathrm { H } _ { 2 } \mathrm { SO } _ { 3 } {/tex}

B

In aqueous medium {tex}\mathrm{HF}{/tex} is a stronger acid than {tex} \mathrm { HCl } {/tex}

C

{tex} \mathrm { HClO } _ { 4 } {/tex} is a weaker acid than {tex}\mathrm{HClO}_3{/tex}

{tex} \mathrm { HNO } _ { 3 } {/tex} is a stronger acid than {tex} \mathrm { HNO } _ { 2 } {/tex}.

##### Explanation

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Q 14. The stability of dihalides of {tex}\mathrm{Si}{/tex}, {tex}\mathrm{Ge}{/tex}, {tex}\mathrm{Sn}{/tex} and {tex}\mathrm{Pb}{/tex} increases steadily in the sequence

A

{tex} \mathrm { Pb } X _ { 2 } < \mathrm { Sn } X _ { 2 } <\mathrm { Ge } X _ { 2 } < \mathrm { Si } X _ { 2 } {/tex}

B

{tex} \mathrm { Ge } X _ { 2 } < \mathrm { Si } X _ { 2 } < \mathrm { Sn } X _ { 2 } < \mathrm { Pb } X _ { 2 } {/tex}

{tex} \mathrm { Si } X _ { 2 } < \mathrm { Ge } X _ { 2 }< \mathrm { Pb } X _ { 2 } < \mathrm { Sn } X _ { 2 } {/tex}

D

{tex} \mathrm { Si } X _ { 2 } < \mathrm { Ge } X _ { 2 } < \mathrm { Sn } X _ { 2 } < \mathrm { Pb } X _ { 2 } {/tex}.

##### Explanation

The stability of dihalides increases down the group:

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Q 15. Identify the incorrect statement among the following.

A

{tex}\mathrm {Br}_2{/tex} reacts with hot and strong {tex} \mathrm {NaOH} {/tex} solution to give {tex} \mathrm {NaBr} {/tex} and {tex} \mathrm { H } _ { 2 } \mathrm { O } {/tex}.

B

Ozone reacts with {tex} \mathrm { SO } _ { 2 } {/tex} to give {tex} \mathrm { SO } _ { 3 } {/tex}.

C

Silicon reacts with {tex} \mathrm { NaOH } _ { ( a q ) } {/tex} in the presence of air to give {tex} \mathrm { Na } _ { 2 } \mathrm { SiO } _ { 3 } {/tex} and {tex} \mathrm { H } _ { 2 } \mathrm { O } {/tex}.

{tex} \mathrm { Cl } _ { 2 } {/tex} reacts with excess of {tex} \mathrm { NH } _ { 3 } {/tex} to give {tex} \mathrm { N } _ { 2 } {/tex} and {tex} \mathrm { HCl } {/tex}.

##### Explanation

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Q 16. In context with the industrial preparation of hydrogen from water gas {tex} \left( \mathrm { CO } + \mathrm { H } _ { 2 } \right) , {/tex} which of the following is the correct statement?

{tex} \mathrm { CO} {/tex} is oxidised to {tex} \mathrm { CO } _ { 2 } {/tex} with steam in the presence of a catalyst followed by absorption of {tex} \mathrm { CO } _ { 2 } {/tex} in alkali

B

{tex}\mathrm { CO}{/tex} and {tex} \mathrm { H } _ { 2 } {/tex} are fractionally separated using differences in their densities

C

{tex}\mathrm{CO}{/tex} is removed by absorption in aqueous {tex} \mathrm { Cu } _ { 2 } \mathrm { Cl } _ { 2 } {/tex} solution

D

{tex} \mathrm { H } _ { 2 } {/tex} is removed through occlusion with {tex} \mathrm { Pd } {/tex}

##### Explanation

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Q 17. Which of the following statements is true?

A

{tex}\mathrm{HF}{/tex} is less polar than {tex}\mathrm{HBr}{/tex}

B

Absolutely pure water does not contain any ions

Chemical bond formation takes place when forces of attraction overcome the forces of repulsion

D

In covalency transference of electron takes place.

##### Explanation

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Q 18. When {tex} \mathrm { H } _ { 2 } \mathrm { S } {/tex} is passed through {tex} \mathrm { Hg } _ { 2 } \mathrm { S } {/tex} we get

A

{tex} \mathrm { HgS } {/tex}

B

{tex} \mathrm { HgS } + \mathrm { Hg } _ { 2 } \mathrm { S } {/tex}

{tex} \mathrm { Hg } _ { 2 } \mathrm { S } + \mathrm { Hg } {/tex}

D

{tex} \mathrm { Hg } _ { 2 } \mathrm { S } {/tex}.

##### Explanation

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Q 19. Which one of the following pairs of molecules will have permanent dipole moments for both members?

A

{tex} \mathrm { SiF } _ { 4 } {/tex} and {tex} \mathrm { NO } _ { 2 } {/tex}

B

{tex} \mathrm { NO } _ { 2 } {/tex} and {tex} \mathrm { CO } _ { 2 } {/tex}

{tex} \mathrm { NO } _ { 2 } {/tex} and {tex} \mathrm { O } _ { 3 } {/tex}

D

{tex} \mathrm { SiF } _ { 4 } {/tex} and {tex} \mathrm { CO } _ { 2 } {/tex}.

##### Explanation

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Q 20. What may be expected to happen when phosphine gas is mixed with chlorine gas?

A

The mixture only cools down

B

{tex} \mathrm { PCl } _ { 3 } {/tex} and {tex} \mathrm { HCl } {/tex} are formed and the mixture warms up

{tex} \mathrm { PCl } _ { 5 } {/tex} and {tex} \mathrm { HCl } {/tex} are formed and the mixture cools down

D

{tex} \mathrm { PH } _ { 3 }.\mathrm { Cl } _ { 2 } {/tex} is formed with warming up.

##### Explanation

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Q 21. In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to

A

generate heat

create potential difference between the two electrodes

C

produce high purity water

D

remove adsorbed oxygen from electrode surface.

##### Explanation

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Q 22. The number of hydrogen atom(s) attached to phosphorus atom in hypophosphorous acid is

A

{tex} \mathrm { Zero} {/tex}

{tex} \mathrm { two } {/tex}

C

{tex} \mathrm { one} {/tex}

D

{tex} \mathrm { three} {/tex}

##### Explanation

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Q 23. Among the following substituted silanes the one which will give rise to cross linked silicone polymer on hydrolysis is

A

{tex} \mathrm { R } _ { 3 } \mathrm { SiCl } {/tex}

B

{tex}\mathrm R _ { 4 }\mathrm S \mathrm i {/tex}

{tex} \mathrm { RSiCl } _ { 3 } {/tex}

D

{tex} \mathrm { R } _ { 2 } \mathrm { SiCl } _ { 2 } {/tex}