Practice problems on JEE Mains, JEE Mains 2021 July 27 Shift 1

Question 1

The parameters of the unit cell of a substance are a=2.5, b=3.0,c=4.0,α=90∘,β=120∘,γ=90∘ . The crystal system of the substance is:

Accepted Answer

Monoclinic

Answer

Orthorhombic

Answer

Hexagonal

Answer

Triclinic

Question 2

The probability that a randomly selected 2 -digit number belongs to the set {n∈N:(2n−2) is a multiple of 3} is equal to:

Accepted Answer

1/2

Answer

1/3

Answer

2/3

Answer

1/6

Question 3

Which one of the following statements is NOT correct?

Accepted Answer

Eutrophication leads to increase in the oxygen level in water

Answer

Eutrophication indicates that water body is polluted

Answer

Eutrophication leads to anaerobic conditions

Answer

The dissolved oxygen concentration below 6 ppm inhibits fish growth.

Question 4

Staggered and eclipsed conformers of ethane are:

Accepted Answer

Rotamers

Answer

Mirror images

Answer

Polymers

Answer

Enantiomers

Question 5

The correct order of stability of given carbocations is:

Accepted Answer

A > C > B > D

Answer

D > B > A > C

Answer

C > A > D > B

Answer

D > B > C > A

Question 6

Given below are two statements:Statement -1: Rutherford's gold foil experiment cannot explain the line spectrum of hydrogen atom.Statement - II : Bohr's model of hydrogen atom contradicts Heisenberg's uncertainty principle.In the light of the above statements, choose the most appropriate answer from the options given below

Accepted Answer

Both statement I and statement II are true.

Answer

Statement I is false but statement II is false.

Answer

Statement I is true but statement II is false.

Answer

Both statement I and statement II are false.

Question 7

The product obtained from the electrolytic oxidation acidified sulphate solution is :

Accepted Answer

HO3​SOOSO3​H

Answer

HO3​SOSO3​H

Answer

HSO4−​

Answer

HO2​SOSO2​H

Question 8

Let C be the set of all complex numbers. Let ​S1​={z∈C∥z−3−2i∣2=8}S2​={z∈C∣Re(z)≥5} and S3​={z∈C∥z−zˉ∣≥8}​ Then the number of elements in S1​∩S2​∩S3​ is equal to:

Accepted Answer

1

Answer

Infinite

Answer

0

Answer

2

Question 9

The figure shows two solid discs with radius R and r respectively. If mass per unit area is same for both, what is the ratio of Ml of bigger disc around axis AB (which is ⊥ to the plane) of the disc and passing through its centre) to MI of smaller disc around one of its diameters lying on its plane ? Given 'M' is the mass of the larger disc. (MI stands for moment of inertia)

Accepted Answer

2R4:r4

Answer

2R2:r2

Answer

R2:r2

Answer

2r4:R4

Question 10

The compound ‘A’ is a complementary base of ________ in DNA strands.

Accepted Answer

Adenine

Answer

Uracil

Answer

Cytosine

Answer

Guanine

Question 11

Given below are two statements:Statements-I : Aniline is less basic than acetamide.Statements-II : In aniline, the lone pair of electrons on nitrogen atom is delocalised over benzene ring due to resonance and hence less available to a proton.Choose the most appropriate option.

Accepted Answer

Statement I is false but statement II is true

Answer

Statement I is true but statement II is false

Answer

Both statements I and statement II are false

Answer

Both statements I and statement II are true

Question 12

A light cylindrical vessel is kept on a horizontal surface. Area of base is A. A hole of cross sectional area ' a ' is made just at the bottom side. The minimum coefficient of friction necessary to prevent sliding the vessel due to the impact force of the emerging liquid is (a≪A):

Accepted Answer

a2a​

Answer

None of these

Answer

Aa​

Answer

2aA​