p-Block Elements — Page 3 | JEE Chemistry

Q21

In a molecule of pyrophosphoric acid, the number of P - OH, P = O and P - O - P bonds/moiety(ies) respectively are :

A 4, 2 and 0

B 4, 2 and 1

C 3, 3 and 3

D 2, 4 and 1

Correct Answer

Option B

Solution

Pyrophosphoric acid Number of P - OH bonds = 4 P = O bonds = 2 P – O – P bonds = 1

Q22

The reaction of H3N3B3Cl3 (A) with LiBH4 in tetrahydrofuran gives inorganic benzene (B). Further, the reaction of (A) with (C) leads to H3N3B3(Me)3. Compounds (B) and (C) respectively, are :

A Borazine and MeBr

B Diborane and MeMgBr

C Boron nitride and MeBr

D Borazine and MeMgBr

Correct Answer

Option D

Solution

B3N3H3Cl3(A) + LiBH4 $\to$ B3N3H6 (B) B = inorganic benzene or Borazine B3N3H3Cl + MeMgBr(C) $\to$ B3N3H3(CH3)3 + 3MgBrCl

Q23

On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with H2 in the presence of a catalyst gives another gas (C) which is basic in nature. (A) should not be :

A Pb(NO3)2

B (NH4)2Cr2O7

C NH4NO2

D NaN3

Correct Answer

Option A

Solution

Basic gas (C) must be ammonia (NH3). It means (B) gas should be N2 which is formed by heating of compound (A). 2Pb(NO3)2

\overset{\Delta}\longrightarrow

2PbO + 4NO2 + O2 (NH4)2Cr2O7

\overset{\Delta}\longrightarrow

N2 $\uparrow$ + Cr2O3 + 4H2O $\uparrow$ NH4NO2

\overset{\Delta}\longrightarrow

N2 $\uparrow$ + 2H2O $\uparrow$ 2NaN3

\overset{\Delta}\longrightarrow

2Na + 3N2 $\uparrow$

Q24

The correct statement with respect to dinitrogen is :

A N2 is paramagnetic in nature

B it can be used as an inert diluent for reactive chemicals

C it can combine with dioxygen at 25oC

D liquid dinitrogen is not used in cryosurgery

Correct Answer

Option B

Solution

(1) N2 is diamagnetic, with no unpaired elctrons.

(2) In iron and chemical Industry because of its inertness it is used where an inert atmosphere is required.

(3) N2 does not combine with oxygen, hydrogen or most other elements.

Nitrogen will combine with oxygen, however in the presence of lightining or a spark.

(4) Liquid nitrogen is used as a refrigerant to preserve biological material food items and in cryosurgery.

Q25

In XeF2, XeF4, XeF6 the number of lone pairs of Xe are respectively :

A 2, 3, 1

B 1, 2, 3

C 4, 1, 2

D 3, 2, 1

Correct Answer

Option D

Solution

In the formation of

Xe{F_2},\,s{p^3}d\,\,

hybridisation occurs which gives the molecule a trigonal bipyramidal structure. In the formation of

Xe{F_4},\,s{p^3}{d^2}

hybridization occurs which gives the molecule an octahedral structure. In the formation of

Xe{F_6},\,s{p^3}{d^3}

hybridization occurs which gives the molecule a pentagonal bipyramidal structure.

Q26

In case of nitrogen, NCl3 is possible but not NCl5 while in case of phosphorous, PCl3 as well as PCl5 are possible. It is due to :

A availability of vacant d orbitals in P but not in N

B lower electronegativity of P than N

C lower tendency of H - bond formation in P than N

D occurrence of P in solid while N in gaseous state at room temperature

Correct Answer

Option A

Solution

{}_7N = 1{s^2}2{s^2}\,2{p^3};\,

\,\,\,\,\,\,\,\,\,\,\,\,\,\,{}_{15}P = 1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}

NOTE : In phosphorous the

3d

-orbitals are available.

Hence phosphorous can from pentahalides also but nitrogen can not form pentahalide due to absence of

d

-orbitals.

Q27

When H2S is passed through Hg2S we get :

A HgS

B HgS + Hg2S

C Hg2S

D Hg2S2

Correct Answer

Option B

Solution

When H2S is passed through Hg2S we get a mixture of mercurous sulphide and mercury(HgS + Hg2S).

Q28

Oxidation number of Cl in CaOCl2 (bleaching powder) is :

A zero, since it contains Cl2

B -1, since it contains Cl-

C +1, since it contains ClO-

D +1 and -1 since it contains ClO- and Cl-

Correct Answer

Option D

Solution

CaOC{l_2} -

or it can also be written as

Ca\mathop {\left( {OCl} \right)}\limits_{{x_1}} \mathop {Cl}\limits_{{x_2}}

hence oxidation no of

Cl

in

OC{l^ - }

is

\begin{aligned}& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, - 2 + {x_2} = - 1 \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{x^2} = 2 - 1 = + 1\end{aligned}

now oxidation no. of another

Cl

is

-1

as it is present as

C{l^ - }.

Q29

Concentrated hydrochloric acid when kept in open air sometimes produces a cloud of white fumes. The explanation for it is that :

A oxygen in air reacts with the emitted HCI gas to form a cloud of chlorine gas

B strong affinity of HCI gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke

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

D concentrated hydrochloric acid emits strongly smelling HCI gas all the time.

Correct Answer

Option A

Solution

4HCl + \mathop {{O_2}}\limits_{air} \to \mathop {2C{l_2} + 2{H_2}O}\limits_{cloud\,\,\,of\,\,\,white\,\,\,fumes}

Q30

Glass is a :

A super-cooled liquid

B gel

C polymeric mixture

D micro-crystalline solid

Correct Answer

Option A

Solution

Glass is a translucent or transparent amorphous super-cooled solid solution or we can say super cooled liquid of silicates and borats having a general formula

{R_2}O.\,MO.\,6Si{O_2}.

where

R=Na

or

K

and

M

=Ca, Ba, Zn

or

Pb.