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## Friday, 29 January 2021

### CBSE Class 12 Chemistry - MCQ and Online Tests - Unit 2 - Solutions

#### CBSE Class 12 Chemistry – MCQ and Online Tests – Unit 2 – Solutions

Every year CBSE conducts board exams for 12th standard. These exams are very competitive to all the students. So our website provides online tests for all the 12th subjects. These tests are also very effective and useful for those who preparing for competitive exams like NEET, JEE, CA etc. It can boost their preparation level and confidence level by attempting these chapter wise online tests.

These online tests are based on latest CBSE Class 12 syllabus. While attempting these our students can identify the weak lessons and continuously practice those lessons for attaining high marks. It also helps to revise the NCERT textbooks thoroughly.

#### CBSE Class 12 Chemistry – MCQ and Online Tests – Unit 2 – Solutions

Question 1.
Henry’s law constant for molality of methane is benzene at 298 K is 4.27 × 105 mm Hg. The mole fraction of methane is nenzene at 298 K under 760 mm Hg is
(a) 1.78 × 10-3
(b) 17.43
(c) 0.114
(d) 2.814

Question 2.
At equilibrium the rate of dissociation of a solid solute in a volatile liquid solvent is
(a) less than the rate of crystallisation
(b) greater than the rate of crystallisation
(c) equal to the rate of crystallisation
(d) zero

Answer: (c) equal to the rate of crystallisation

Question 3.
The system that forms maximum boilingazetrope is
(a) Acetone-chloroform
(b) ethanol-acetone
(c) n-hexane-n-heptane
(d) carbon disulphide-acetone

Question 4.
3 moles of P and 2 moles of Q are mixed, what will be their total vapour pressure in the solution if their partial vapour pressures are 80 and 60 torr respectively?
(a) 80 torr
(b) 140 torr
(c) 72 torr
(d) 70 torr

Question 5.
How much oxygen is dissolved in 100 rnL water at 298 K if partial pressure of oxygen is 0.5 atm and K = 1.4 × 10-3 mol/L/atm?
(a) 22.4 mg
(b) 22.4 g
(c) 2.24 g
(d) 2.24 mg

Question 6.
Among the following substances the lowest vapour pressure is exerted by
(a) water
(b) alcohol
(c) ether
(d) mercury

Question 7.
Vapour pressure of a pure liquid X is 2 atm at 300 K. It is lowered to 1 atm on dissolving 1 gof Y in 20 g of liquid X. If molar mass of X is 200, what is the molar mass of Y?
(a) 20
(b) 50
(c) 100
(d) 200

Question 8.
If 2 gm of NaOH is present is 200 ml of its solution, its molarity will be
(a) 0.25
(b) 0.5
(c) 5
(d) 10

Question 9.
Partial pressure of a solution component is directly proportional to its mole fraction. This is known as
(a) Henry’s law
(b) Raoult’s law
(c) Distribution law
(d) Ostawald’s dilution law

Question 10.
Which of the following solutions shows positive deviation from Raoult’s law?
(a) Acetone + Aniline
(b) Acetone + Ethanol
(c) Water + Nitric acid
(d) Chloroform + Benzene

Question 11.
A plant cell shrinks when it is kept in a
(a) hypotonic solution
(b) hypertonic solution
(c) isotonic solution
(d) pure water

Question 12.
A solution containing 10.2 g glycerine per litre is isotonic with a 2% solution of glucose. What is the molecular mass of glycerine?
(a) 91.8 g
(b) 1198 g
(c) 83.9 g
(d) 890.3 g

Question 13.
The osmotic pressure of a solution can be increased by
(a) increasing the volume
(b) increasing the number of solute molecules
(c) decreasing the temperature
(d) removing semipermeable membrane

Answer: (b) increasing the number of solute molecules

Question 14.
The atmospheric pollution is generally measured in the units of
(a) mass percentage
(b) volume percentage
(c) volume fraction
(d) ppm

Question 15.
Sprinkling of salt helps in clearing the snow covered roads in hills. The phenomenon involved in the process is
(a) lowering in vapour pressure of snow
(b) depression in freezing point of snow
(c) melting of ice due to increase in temperature by putting salt
(d) increase in freezing point of snow

Answer: (b) depression in freezing point of snow

Question 16.
What weight of glycerol should be added to 600 g of water in order to lower its freezing point by 10°C ?
(a) 496 g
(b) 297 g
(c) 310 g
(d) 426 g

Question 17.
The law which indicates the relation’-hip between solubility of a gas in liquid and pressure rs
(a) Raoult’s law
(b) Henry’s law
(c) Lowering of vapour pressure
(d) Van’t Hoff law

Question 18.
A 5% solution of cane-sugar (molecular weight = 342) is isotonic with 1% solution of substance A. The molecular weight of X is
(a) 342
(b) 171.2
(c) 68.4
(d) 136.8

Question 19.
The relative lowering in vapour pressure is proportional to the ratio of number of
(a) solute molecules to solvent molecules
(b) solvent molecules to solute molecules
(c) solute molecules to the total number of molecules in solution
(d) solvent molecules to the total number of molecules in solution

Answer: (c) solute molecules to the total number of molecules in solution

Question 20.
For carrying reverse osmosis for desalination of water the material used for making semipermeable membrane is
(a) potassium nitrate
(b) parchment membrane
(c) cellulose acetate
(d) cell membrane

Question 21.
H2S is a toxic gas used in qualitative analysis. If solubility of H2S in water at STP is 0.195 m. what is the value of KH?
(a) 0.0263 bar
(b) 69.16 bar
(c) 192 bar
(d) 282 bar

Question 22.
Atomic mass is equal to
(a) number of electrons of an atom
(b) sum of the numbers of electrons and protons of an atom
(c) sum of the numbers of neutrons and protons of an atom
(d) none of these

Answer: (b) sum of the numbers of electrons and protons of an atom

Question 23.
What will be the degree of dissociation of 0.1 M Mg(NO3)2 solution if van’t Hoff factor is 2.74?
(a) 75%
(b) 87%
(c) 100%
(d) 92%

Question 24.
Which of the following units is useful in relating concentration of solution with its vapour pressure?
(a) Mole fraction
(b) Parts per million
(c) Mass percentage
(d) Molality

Question 25.
234.2 gm of sugar syrup contains 34.2 gm of sugar. What is the molal concentration of the solution.
(a) 0.1
(b) 0.5
(c) 5.5
(d) 55

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