Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

For principle quantum number n = 4, the total number of orbitals having l= 3 is

  • 3

  • 7

  • 5

  • 9


B.

7

n=4

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14

l = 3 only for f orbital.Thus the total number of orbitals for l = 3 is equal to 7 (because f contains seven orbitals).


2.

The statement true for N3- is

  • it has a non-linear structure

  • it is called pseudohalogen

  • the formal oxidation state of nitrogen in this anion is -1

  • it is isoelectronic with NO2


C.

the formal oxidation state of nitrogen in this anion is -1

Azide ion is a linear molecule, it is a pseudo halide and formal oxidation state of N in azide ion is -1.

N3-: :N....-N+..N:  :NN+..-N....: :N-..=Nmajor+=N:..-


3.

Dimethyl glyoxime gives a red precipitate with Ni2+, which is used for its detection. To get this precipitate readily the best pH range is

  • < 1

  • 2-3

  • 3- 4

  • 9- 11


D.

9- 11

Nickel(II) forms a precipitate with the organic compound dimethylglyoxime, C4H6(NOH)2. The formation of the red chelate occurs quantitatively in a solution in which the pH is buffered in the range of 5 to 9. The chelation reaction that occurs is illustrated below.

The reaction is performed in a solution buffered by either an ammonia or citrate buffer to prevent the pH of the solution from falling below 5. If the pH does become too low the equilibrium of the above reaction favors the formation of nickel(II) ion, causing the dissolution of Ni(DMG)2 back into the mother liquor.


4.

The compound insoluble in water is

  • mercurous nitrate

  • mercuric nitrate

  • mercurous chloride

  • mercurous perchlorate.


C.

mercurous chloride

According to "solubility rule" following compounds are soluble in water:
(i) All common group IA and NH4+ compounds.
(ii) All common NO3- (nitrate), CH3COO-(acetate), ClO4, (perchlorate) compounds.
(iii) All common Cl- , Br- , I- compounds, except those of Ag+, Pb2+,Cu+ and Hg22+(mercurous)
(iv) All common SO42- (sulphate) compounds, except those of Ca2+, Sr2+, Ba2+ and Pb2+.


5.

Shape of O2F2 is similar to that of

  • C2F2

  • H2O2

  • H2F2

  • C2H2


B.

H2O2

O2Fand H2O2, both have open book type structure.

In O2F2, one O-O bond and two O-F are lying in different plane, i.e this molecule like H2O2 has non- linear and non- planar structure.


6.

The liquefied metal expanding on solidification is

  • Ga

  • Al

  • Zn

  • Cu.


A.

Ga

Gallium is brittle at low temperature but is liquid above room temperature and can indeed melt in the hand. Gallium metal expands by 3.1 percent when it solidifies, and  therefore should not be stored in either glass or metal containers. Gallium also corrodes most other metals by diffusing into their metal lattice.


7.

The ONO angle is maximum in

  • NO3-

  • NO2-

  • NO2

  • NO2+


D.

NO2+

The nitrate ion has three resonance structure, with the double bond on a different oxygen for each. In all resonance structures the nitrogen has three bonds, therefore, its hybridisation is sp2. Each of the oxygen atoms also has sp2 hybridisation, since the hybridisation is determined by the resonance structure with the double bond, where the oxygen has a double bond and two lone pairs.

The actual geometry of the polyatomic ion is trigonal planar with bond angles of 120°,

NO2-:18 electrons; ideal geometry trigonal planar, sp2 with bond angle of 116°.

NO2 : 17 electrons, ideal geometry trigonal planar; sp2 with bond angle of 134°.

NO2+: 16 electrons; ideal geometry linear ; sp with bond angle of 180°,

               O....=N+=O....


8.

How much energy is released when 6 moles of octane is burnt in air? Given Hf° for CO2(g) , H2O(g) and C8H18(l)  respectively are - 490, -240 and +160 kJ/mol.

  • -6.2 kJ

  • -37.4 kJ

  • -35.5 kJ

  • -20.0 kJ


B.

-37.4 kJ

C +O2  CO2 ; Hf° =-490 kJ/ mol ×8H2 + 12O2 H2O  ; Hf° = -240 kJ/mol ×98C +18H  C8H18 ; Hf° = +160 kJ/mol8C+ 8O2 + 9H2+92O2-8C -18H  8CO2 +9H2O-C8H18                                                                 Hf°= -3920-2160-160C8H8 +252O2 8CO2 + 9H2O ; H°= -6240kJ/molH° for 6 moles of octane= -6240 × 6= -37440 kJ/mol.


9.

For the equilibrium H2O(l)  H2O(g) at 1 atm and 298K.

  • standard free energy change is equal to zero (G°= 0)

  • free energy change is less than zero (G° < 0)

  • standard free energy change is less than zero (G°< 0)

  • standard free energy change is greater than zero (G° > 0).


A.

standard free energy change is equal to zero (G°= 0)

H2O(l)  H2O(g)

This is a spontaneous process at standard conditions thus, the standard free energy change must be less then zero, i.e. G° < 0.


10.

The dipole moment is the highest for

  • trans-2-butene

  • 1,3-dimethylbenzene

  • acetophenone

  • ethanol.


C.

acetophenone

The value of dipole moment of acetophenone is 3 debye, which is maximum among the given compounds.