List of top Questions asked in JEE Main

Flocculation value of \(\mathrm{BaCl_2}\) is much less than that of \(\mathrm{KCl}\) for sol A and flocculation value of \(\mathrm{Na_2SO_4}\) is much less than that of \(\mathrm{NaBr}\) for sol B. The correct statement among the following is :

In Williamson synthesis of mixed ether having a primary and a tertiary alkyl group if tertiary halide is used, then :

Clemmensen reduction of a ketone is carried out in the presence of :

Which of the following would not give 2-phenylbutane as the major product in a Friedel-Crafts alkylation reaction ?

Which one of the following arrangements represents the correct order of solubilities of sparingly soluble salts \(\mathrm{Hg_2Cl_2}\), \(\mathrm{Cr_2(SO_4)_3}\), \(\mathrm{BaSO_4}\) and \(\mathrm{CrCl_3}\) respectively?

NaOH is a strong base. What will be pH of \(5.0\times10^{-2}\) M NaOH solution ? (\(\log 2 = 0.3\))

Values of dissociation constant, \(K_a\) are given as follows :

Acid	\(K_a\)
HCN	\(6.2\times10^{-10}\)
HF	\(7.2\times10^{-4}\)
\(\mathrm{HNO_2}\)	\(4.0\times10^{-4}\)

Correct order of increasing base strength of the base \(\mathrm{CN^-}\), \(\mathrm{F^-}\) and \(\mathrm{NO_2^-}\) will be :

The solubility order for alkali metal fluoride in water is :

The half-life of a radioactive element A is the same as the mean-life of another radioactive element B. Initially both substances have the same number of atoms, then :

The wave number of the first emission line in the Balmer series of H-Spectrum is : (\(R\) = Rydberg constant)

The reaction \(\mathrm{X} \to \mathrm{Y}\) is an exothermic reaction. Activation energy of the reaction for X into Y is 150 kJ mol^-1. Enthalpy of reaction is 135 kJ mol^-1. The activation energy for the reverse reaction, \(\mathrm{Y} \to \mathrm{X}\) will be :

Given

Reaction	Energy Change (in kJ)
\(\mathrm{Li(s)} \to \mathrm{Li(g)}\)	161
\(\mathrm{Li(g)} \to \mathrm{Li^+(g)}\)	520
\(\frac{1}{2}\mathrm{F_2(g)} \to \mathrm{F(g)}\)	77
\(\mathrm{F(g)} + \mathrm{e^-} \to \mathrm{F^-(g)}\)	(Electron gain enthalpy)
\(\mathrm{Li^+(g)} + \mathrm{F^-(g)} \to \mathrm{LiF(s)}\)	\(-1047\)
\(\mathrm{Li(s)} + \frac{1}{2}\mathrm{F_2(g)} \to \mathrm{LiF(s)}\)	\(-617\)

Based on data provided, the value of electron gain enthalpy of fluorine would be :

Bond order normally gives idea of stability of a molecular species. All the molecules viz. \(\mathrm{H_2}\), \(\mathrm{Li_2}\) and \(\mathrm{B_2}\) have the same bond order yet they are not equally stable. Their stability order is :

The focal length of the objective and the eyepiece of a telescope are 50 cm and 5 cm respectively. If the telescope is focussed for distinct vision on a scale distant 2 m from its objective, then its magnifying power will be :

Orbits of a particle moving in a circle are such that the perimeter of the orbit equals an integer number of de-Broglie wavelengths of the particle. For a charged particle moving in a plane perpendicular to a magnetic field, the radius of the \(n^{\mathrm{th}}\) orbital will therefore be proportional to :

This question has Statement-1 and Statement-2. Of the four choices given after the Statements, choose the one that best describes the two Statements.
Statement-1: In Young's double slit experiment, the number of fringes observed in the field of view is small with longer wavelength of light and is large with shorter wavelength of light.
Statement-2: In the double slit experiment the fringe width depends directly on the wavelength of light.

This question has Statement-1 and Statement-2. Of the four choices given after the Statements, choose the one that best describes the two Statements.
Statement-1: Short wave transmission is achieved due to the total internal reflection of the e-m wave from an appropriate height in the ionosphere.
Statement-2: Refractive index of a plasma is independent of the frequency of e-m waves.

An LCR circuit as shown in the figure is connected to a voltage source \(V_{ac}\) whose frequency can be varied.

(Circuit: inductor 24 H, capacitor 2 \(\mu\)F and resistor 15 \(\Omega\) in series with the source \(V_{ac} = V_0 \sin\omega t\); a voltmeter V is connected across the resistor.)
The frequency, at which the voltage across the resistor is maximum, is :

In a series L - C - R circuit, \(C = 10^{-11}\) Farad, \(L = 10^{-5}\) Henry and \(R = 100\) Ohm, when a constant D.C. voltage \(E\) is applied to the circuit, the capacitor acquires a charge \(10^{-9}\) C. The D.C. source is replaced by a sinusoidal voltage source in which the peak voltage \(E_0\) is equal to the constant D.C. voltage \(E\). At resonance the peak value of the charge acquired by the capacitor will be :

A and B are two sources generating sound waves. A listener is situated at C. The frequency of the source at A is 500 Hz. A, now, moves towards C with a speed 4 m/s. The number of beats heard at C is 6. When A moves away from C with speed 4 m/s, the number of beats heard at C is 18. The speed of sound is 340 m/s.

The frequency of the source at B is :

A mass \(m=1.0\) kg is put on a flat pan attached to a vertical spring fixed on the ground. The mass of the spring and the pan is negligible. When pressed slightly and released, the mass executes simple harmonic motion. The spring constant is 500 N/m. What is the amplitude A of the motion, so that the mass \(m\) tends to get detached from the pan ? (Take \(g=10\ \mathrm{m/s^2}\) ). The spring is stiff enough so that it does not get distorted during the motion.

A point charge of magnitude \(+1\,\mu\mathrm{C}\) is fixed at \((0,0,0)\). An isolated uncharged spherical conductor, is fixed with its center at \((4,0,0)\). The potential and the induced electric field at the centre of the sphere is :

A current \(i\) is flowing in a straight conductor of length \(L\). The magnetic induction at a point on its axis at a distance \(\frac{L}{4}\) from its centre will be :

A dc source of emf \(E_1=100\) V and internal resistance \(r=0.5\ \Omega\), a storage battery of emf \(E_2=90\) V and an external resistance R are connected as shown in figure. For what value of R no current will pass through the battery?

To find the resistance of a galvanometer by the half deflection method the following circuit is used with resistances \(R_1=9970\ \Omega\), \(R_2=30\ \Omega\) and \(R_3=0\). The deflection in the galvanometer is d. With \(R_3=107\ \Omega\) the deflection changed to \(\frac d2\). The galvanometer resistance is approximately: