Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

According to Bohr's theory, which of the following correctly represents the variation of energy and radius of an electron in nth orbit of H-atom?

  • En  1n2, r 1n2

  • En 1n2, r n2

  • En n2, r n2

  • En n, r 1n


B.

En 1n2, r n2

According to Bohr's theory,

r = n2h24π2mZe2k and En-k22π2mZ2e4n2h2

Therefore, E1n2and r n2


2.

An element (X) belongs to fourth period and fifteenth group of the periodic table. Which one of the following is true regarding the outer electronic configuration of (X)? It has

  • partially filled d orbitals and completely filled s orbital

  • completely filled s orbital and completely filled p orbitals

  • completely filled s orbital and half-filled p orbitals

  • half-filled d orbitals and completely filled s orbital.


C.

completely filled s orbital and half-filled p orbitals

The electronic configuration of (X) can be written as

X = 1s22s22p63s23p64s23d104p3

So element (X) has completely filled s orbital and d orbitals and half filled orbitals.


3.

Assertion : H3BOis a weak acid.

Reason : Water extracts the proton of H3BO3.

  • If both assertion and reason are true and reason is the correct explanation of assertion.

  • If both assertion and reason are true but reason is not the correct explanation of assertion.

  • If assertion is true but reason is false

  • If both assertion and reason are false.


C.

If assertion is true but reason is false

H3BO3 is a very weak monobasic acid (Ka= 5.6 × 10-10) but it does not act as a proton donor. It behaves as a Lewis acid i.e., it accepts a pair of electrons from OH- ion of H2O.

H - OH + B(OH)3  [B(OH)4]- + H+


4.

Best reagent for the conversion of AgNO3 to Ag is

  • HClO4

  • H3PO2

  • HIO4

  • I2


B.

H3PO2

H3PO2 is a good reducing agent as it contains two P-H bonds and thus reduces AgNO3 to Ag.

4AgNO3 + H3PO2 + 2H2 4Ag  + H3PO4 + 4HNO3


5.

10 ml of liquid carbon disulphide (specific gravity 2.63) is burnt in oxygen. Find the volume of the resulting gases measured at STP.

  • 23.25 L

  • 22.26 L

  • 23.50 L

  • 20.08 L


A.

23.25 L

1 mL of CS2 weighs 2.63 gm

10 mL of CS2 weighs 26.3 gm

CS212 + (2 × 32)76 gm + O2    CO222.4 L + 2SO244.8 L67.2 L

 76 gm of CS2 will yield 67.2 L of a mixture of CO2 and SO2 at STP.

 26.3 gm of CS2 would yield 67.276 × 26.3 = 23.25 L


6.

KP for the reaction A  B is 4. If initially only A is present then what will be the partial pressure of B after equilibrium?

  • 1.2

  • 0.8

  • 0.6

  • 1


B.

0.8

Assuming that reaction is started with 1 mol of A and at equilibrium x moles of A have reacted,

   A1 mol1-x mol  B0 (initially)x mol (at equilibrium)

KppBpA= 4

    = x1-x = 4

 x = 0.8


7.

Which of the following reactions does not take place?

BF3 + F- BF4-          ...(I)

BF3 + 3F- BF63-       ...(II)

AlF3 + 3F-  AlF63-    ...(III)

  • Only (I)

  • Only (II)

  • Only (III)

  • Only (I) and (III)


B.

Only (II)

BF3 forms complex halides of the type [BF4-] in which B atom has C.N. 4, it cannot extend its C.N. beyond 4 due to the non-availability of d-orbitals in its configuration. Hence, BF63- ion (sp3d2 hybridisation) is not formed. On the other hand, Al can extend its C.N. beyond 4 due to the availability of d-orbitals in its configuration.


8.

Which of the following molecules has more than one lone pair ?

  • SO2

  • XeF2

  • SiF4

  • CH4


B.

XeF2

Among all the given options, XeF2 has more than one lone pair, i.e. 3.

 

SO2 has one lone pair.

SiF4 and CH4 has no lone pairs.


9.

The true statement for the acids of phosphorus, H3PO2 H3PO3 and H3PO4 is

  • the order of their acidity is H3PO4 > H3PO3 > H3PO2

  • all of them are reducing in nature

  • all of them are tribasic acids

  • the geometry of phosphorus is tetrahedral in all the three.


D.

the geometry of phosphorus is tetrahedral in all the three.

H3PO2, H3PO3 and H3PO4 contain one, two and three ionisable hydrogen atoms respectively.

H3PO2 H+ + H2PO2-

H3PO3  H+ H2PO3-  H+ + HPO32-

H3PO4  H+ + H2PO4-  H+ + HPO42-

                                     H+ + PO43-

But there is very little difference in acidity. In H3PO2, H3PO3 and H3PO4, P is sp3 hybridised in all. Therefore, all are tetrahedral.


10.

Four diatomic species are listed below in different sequences. Which of these represents the correct order of their increasing bond order?

  • C22- < He2+ < NO < O2-

  • He2+ < O2- < NO < C22-

  • O2- < NO < C22- < He2+

  • NO < C22- < O2- < He2+


B.

He2+ < O2- < NO < C22-

According to molecular orbital theory, the energy level of the given molecules are

C22-  σ1s2 σ*1s2 σ2s2 σ*2s2 π2px2 π2py2 σ2pz2

Bond Order : 12[10 - 4] = 3

He2+  σ1s2 σ*1s1

Bond Order : 122 - 1 = 12 = 0.5

 NO  σ1s2 σ*1s2 σ2s2 σ*2s2 σ2pz2 π2px2 π2py2 π*2px1

Bond Order : 1210 - 5 = 2.5

O2-  σ1s2 σ*1s2 σ2s2 σ*2s2 σ2pz2 π2px2 π2py 2π*2px2 π*2py1

Bond Order : 1210 - 7 = 1.5

So, the correct order of their increasing bond order is He2+ < O2- < NO<C22-