List of top Questions asked in JEE Main- 2021

Two cars X and Y are approaching each other with velocities 36 km/h and 72 km/h respectively. The frequency of a whistle sound as emitted by a passenger in car X, heard by the passenger in car Y is 1320 Hz. If the velocity of sound in air is 340 m/s, the actual frequency of the whistle sound produced is _________ Hz.
First, a set of n equal resistors of 10 \(\Omega\) each are connected in series to a battery of emf 20 V and internal resistance 10 \(\Omega\). A current I is observed to flow. Then, the n resistors are connected in parallel to the same battery. It is observed that the current is increased 20 times, then the value of n is _________.
A uniform conducting wire of length is 24a, and resistance R is wound up as a current carrying coil in the shape of an equilateral triangle of side 'a' and then in the form of a square of side 'a'. The coil is connected to a voltage source V\(_0\). The ratio of magnetic moment of the coils in case of equilateral triangle to that for square is 1 : \(\sqrt{y}\) where y is _________.
The alternating current is given by \(i = \{\sqrt{42} \sin(\frac{2\pi}{T}t) + 10\} A\). The r.m.s. value of this current is _________ A.
A transmitting antenna has a height of 320 m and that of receiving antenna is 2000 m. The maximum distance between them for satisfactory communication in line of sight mode is 'd'. The value of 'd' is _________ km. (Radius of Earth = 6400 km)

A rod CD of thermal resistance 10.0 KW\(^{-1}\) is joined at the middle of an identical rod AB as shown in figure. The ends A, B and D are maintained at 200\(^{\circ}\)C, 100\(^{\circ}\)C and 125\(^{\circ}\)C respectively. The heat current in CD is P watt. The value of P is _________. 

 

The unit of the van der Waals gas equation parameter 'a' in \(\left(P + \frac{an^2}{V^2}\right)(V - nb) = nRT\) is:

Match items of List - I with those of List - II: 

Choose the most appropriate answer from the options given below : 
 

Match List - I with List - II : 

Choose the most appropriate answer from the options given below : 
 

Tyndall effect is more effectively shown by:
In which one of the following molecules strongest back donation of an electron pair from halide to boron is expected?
Which refining process is generally used in the purification of low melting metals ?
Deuterium resembles hydrogen in properties but :
The number of water molecules in gypsum, dead burnt plaster and plaster of Paris, respectively are :
In polythionic acid, H\(_2\)S\(_x\)O\(_6\) (x = 3 to 5) the oxidation state(s) of sulphur is/are :
The gas 'A' is having very low reactivity reaches to stratosphere. It is non-toxic and non-flammable but dissociated by UV-radiations in stratosphere. The intermediates formed initially from the gas 'A' are:

In the following sequence of reactions, the final product D is : 

 

In the following sequence of reactions the P is: 

The structure of the starting compound P used in the reaction given below is: 

 

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Synthesis of ethyl phenyl ether may be achieved by Williamson synthesis.
Reason (R): Reaction of bromobenzene with sodium ethoxide yields ethyl phenyl ether.
In the light of the above statements, choose the most appropriate answer from the options given below :

The major product of the following reaction is: 

Which of the following is not a correct statement for primary aliphatic amines?

The correct statement about (A), (B), (C) and (D) is: 

Out of following isomeric forms of uracil, which one is present in RNA? 

Acidic ferric chloride solution on treatment with excess of potassium ferrocyanide gives a Prussian blue coloured colloidal species. It is: