Practice problems on JEE Mains, JEE Mains 2021 Aug 31 Shift 2

Question 1

Which one of the following statements is incorrect?

Accepted Answer

At around 2000 K, the dissociation of dihydrogen into its atoms is nearly 8.1%.

Answer

Bond dissociation enthalpy of H2 is highest among diatomic gaseous molecules which contain a single bond

Answer

Dihydrogen is produced on reacting zinc with HCl as well as NaOH(aq).

Answer

Atomic hydrogen is produced when H2, molecules at a high temperature are irradiated with UV radiation.

Question 2

Statement-I : To get a steady dc output from the pulsating voltage received from a full wave rectifier we can connect a capacitor across the output parallel to the load RL​ .Statement-II : To get a steady dc output from the pulsating voltage received from a full wave rectifier we can connect an inductor in series with RL​ .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

Both Statement-I and Statement-II are false.

Answer

Statement-I is false but Statement-II is true.

Answer

Statement-I is true but Statement-II is false.

Question 3

If VA​ and VB​ are the input voltages (either 5 V or 0 V ) and V0​ is the output voltage then the two gates represented in the following circuits (A) and (B) are :

Accepted Answer

OR and NOT Gate

Answer

AND and NOT Gate

Answer

AND and OR Gate

Answer

NAND and NOR Gate

Question 4

A mixture of hydrogen and oxygen has volume 500 cm3, temperature 300 K , pressure 400kPa and mass 0.76 g. The ratio of masses of oxygen to hydrogen will be :

Accepted Answer

16 : 3

Answer

3 : 8

Answer

3 : 16

Answer

8 : 3

Question 5

The locus of mid-points of the line segments joining (-3,-5) and the points on the ellipse 4x2​+9y2​=1 is:

Accepted Answer

36x2+16y2+108x+80y+145=0

Answer

9x2+4y2+18x+8y+145=0

Answer

36x2+16y2+90x+56y+145=0

Answer

36x2+16y2+72x+32y+145=0

Question 6

The mean and variance of 7 observations are 8 and 16 respectively. If two observations are 6 and 8, then the variance of the remaining 5 observations is

Accepted Answer

536/5

Answer

134/5

Answer

112/5

Answer

92/5

Question 7

Which one of the following correctly represents the order of stability oxides X2O; (X-halogen)?sss

Accepted Answer

I > Cl > Br

Answer

Br > I > Cl

Answer

Br > Cl > I

Answer

CI > I > Br

Question 8

Spin only magnetic moment in BM of [Fe(CO)4​(C2​O4​)]+ is:

Accepted Answer

1.73

Answer

0

Answer

1

Answer

5.92

Question 9

Match List - I with List - II :Choose the most appropriate answer from the options given below:

Accepted Answer

(a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

Answer

(a)-(i), (b)-(iv), (c)-(ii), (d)-(iii)

Answer

(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Answer

(a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)

Question 10

Let A be the set of all points (α,β) such that the area of triangle formed by the points (5,6),(3,2) and (α,β) is 12 square units. Then the least possible length of a line segment joining the origin to a point in A, is

Accepted Answer

5​8​

Answer

5​4​

Answer

5​12​

Answer

5​16​

Question 11

For a body executing S.H.M. :(a) potential energy is always equal to its K.E.(b) Average potential and kinetic energy over any given time interval are always equal.(c) Sum of the kinetic and potential energy at any point of time is constant.(d) Average K.E. in one time period is equal to average potential energy in one time period.Choose the most appropriate option from the options given below :

Accepted Answer

(c) and (d)

Answer

only (b)

Answer

only (c)

Answer

(b) and (c)

Question 12

In which one of the following sets all species show disproportionation reaction?

Accepted Answer

Cr2​O72−​,MnO4−​ClO2−​andCl 2​

Answer

ClO2−​,MnO4−​andCrO 72−​

Answer

MnO4−​,ClO2​ and Mn3+

Answer

ClO4−​,MnO4−​andClO 2−​

Question 13

Which among the following is not a polyester ?

Accepted Answer

Novolac

Answer

Dacron

Answer

PHBV

Answer

Glyptal