Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

21.

The vapour pressure of 100g water reduces from 3000 Nm-2 to 2985 Nm-2 when 5g of substance 'X' is dissolved in it. Substance 'X' is

  • methanol

  • glucose

  • carbon dioxide

  • cannot predict


B.

glucose

p° - psp° = nn + N = wmwm + WM wm < WMp° - psp° = wmWM = wm × MW= 3000 - 29853000 = 5m × 18100m = 5 × 18 ×300015 × 100 = 180

180 is the molecular weight of glucose (C6H12O6), thus the substance X is glucose.


22.

White P reacts with caustic soda, the products are PH3 and NaH2PO2. This reaction is an example of

  • hydrolysis

  • reduction

  • disproportionation

  • neutralisation


C.

disproportionation

The above reaction is an example of disproportionation reaction, i.e. the reaction in which oxidation and reduction take place simultaneously.


23.

If a be the edge length of the unit cell and r be the radius of an atom then for fee arrangement, the correct relation is

  • 4a = 3r

  • 4r = 3a

  • 4r = 2a

  • 4r = a2


C.

4r = 2a

Given, the edge length of the unit cell = a and, radius of the sphere = r

Consider ABC,

AC2 = AB+ AC2

       = a2 + a2

       = 2a2

Therefore, AC = 2a

But, in figure, AC = 4r

Therefore, 4r = 2a


24.

How long it will take to deposit 1.0 g of chromium when a current of 1.25 A flows through a solution of chromium (III) sulphate ? (Molar mass of Cr = 52)

  • 1.24 min

  • 1.24 h

  • 1.24 s

  • None of these


B.

1.24 h

Cr3+ + 3e-  Cr(s)

3 mol or 3 x 96500 C of electricity are needed to deposit 1 mol or 52 g of Cr

52 gm of Cr will require current = 3 x 96500C

1 gm of Cr will require current = 3 × 9650052C = 5567.3C

Now, number of coulombs = current (ampere) x t (seconds)

 Time(s) required = no. of coulombscurrent (ampere)                                 = 5567.3C1.25A                                 = 4453.8 s = 1.24 h


25.

The complex ion which has no d-electrons in the central metal atom is

  • [MnO4]-

  • [Co(NH3)6]3+

  • [Fe(CN)6]3-

  • [Cr(H2O)6]3+


A.

[MnO4]-

In [MnO4]-, the oxidation state of Mn is + 7

Mn(25) = [Ar] 3d54s2

Mn7+ = [Ar]

Thus, in [MnO4]- no d-electron is present.


26.

A solid AB has the NaCl structure. If radius of cation A+ is 120 pm, the maximum possible value of the radius of the anion B- is

  • 240 pm

  • 60 pm

  • 49.6 pm

  • 290 pm


D.

290 pm

For NaCl crystal,

Radius of cation/ radius of anion = 0.414

rA+rB- = 0.414

rB- = rA+0.414 = 1200.414  = 290 ppm


27.

For a reaction, A+ B  Product, the rate is given by,

r = k[A]1/2[B]2

What is the order of the reaction?

  • 0.5

  • 2

  • 2.5

  • 1


C.

2.5

Order of a reaction is the sum of the power to which the concentration terms are raised in the rate law equation to express the observed rate of the reaction

Hence, order = 12 + 2 = 52 = 2.5


28.

Dihedral angle between two methyl groups of n-butane in the gauche and anti forms are

  • 60°, 0°

  • 0°, 60°

  • 60°, 180°

  • 180°, 60°


C.

60°, 180°

The angle between C-C and C-H bonds on adjacent carbon atoms in any conformation is called dihedral angle. Hence, the dihedral angle in case of gauche is 60°and in anti form is 180°.


29.

The solubility of saturated solution of Ag2CrO4 is s mol L-1. What is its solubility product?

  • 4s3

  • s3

  • 2s3

  • 16s2


A.

4s3

Ag2CrO4  2Ag+ + CrO42-

s mol/L      2s mol/L  s mol/L

Hence, the solubility product is

Ksp of Ag2CrO4 = [Ag+]2[CrO42-]

                       = (2s)2(s)

                       = 4s3

Therefore, 4s3 is the solubility product.


30.

The number of phase in a colloidal system is

  • 1

  • 2

  • 3

  • 4


B.

2

Colloidal solution is of heterogeneous nature. It consists oftwo phases ie, a dispersed phase and a dispersion medium.