List of top Questions asked in JEE Main- 2019

The pair of metal ions that can give a spin only magnetic moment of 3.9 BM for the complex \(\mathrm{[M(H_2O)_6]Cl_2}\), is \(-\)

can not be prepared by \(-\)
(The structure shown is \(\mathrm{CH_3CH_2C(OH)(Ph)CH_3}\), i.e. 2-phenylbutan-2-ol.)

The element with Z = 120 (not yet discovered) will be an/a \(-\)

A 100 V carrier wave is made to vary between 160 V and 40 V by a modulating signal. What is the modulation index ?

Decomposition of X exhibits a rate constant of \(0.05\ \mu\mathrm{g/year}\). How many year are required for the decomposition of \(5\ \mu\mathrm{g}\) of X into \(2.5\ \mu\mathrm{g}\)?

The increasing order of reactivity of the following compounds towards reaction with alkyl halides directly is

(The figure shows four structures labelled (A) benzamide, (B) phthalimide, (C) 2-aminobenzonitrile, (D) aniline.)

In the following reaction, products A and B are \(-\)

In the following reaction :
\(\text{Aldehyde} + \text{Alcohol} \xrightarrow{\ \mathrm{HCl}\ } \text{Acetal}\)

Aldehyde	Alcohol
HCHO	tBuOH
\(\mathrm{CH_3CHO}\)	MeOH

The best combination is

A cylinder of radius R is surrounded by a cylindrical shell of inner radius R and outer radius 2R. The thermal conductivity of the material of the inner cylinder is \(K_1\) and the of the outer cylinder is \(K_2\). Assuming no loss of heat, the effective thermal conductivity of the system for heat flowing along the length of the cylinder is :

Two electric bulbs, rated at (25 W, 220 V) and (100 W, 220 V), are connected in series across a 220 V voltage source. If the 25 W and 100 W bulbs draw powers \(P_1\) and \(P_2\) respectively, then :

A light wave is incident normally on a glass slab of refractive index 1.5. If 4 % of light gets reflected and the amplitude of the electric field of the incident light is 30 V/m, then the amplitude of the electric field for the wave propagating in the glass medium will be :

As shown in the figure, two infinitely long, identical wires are bent by \(90^\circ\) and placed in such a way that the segments LP and QM are along the x-axis, while segments PS and QN are parallel to the y-axis. If OP = OQ = 4 cm, and the magnitude of the magnetic field at O is \(10^{-4}\) T, and the two wires carry equal currents (see figure), the magnitude of the current in each wire and the direction of the magnetic field at O will be (\(\mu_0 = 4\pi \times 10^{-7}\ \mathrm{NA^{-2}}\)) :

A particle A of mass 'm' and charge 'q' is accelerated by a potential difference of 50 V. Another particle B of mass '4 m' and charge 'q' is accelerated by a potential difference of 2500 V. The ratio of de-Broglie wavelengths \(\dfrac{\lambda_A}{\lambda_B}\) is close to :

In the figure shown, a circuit contains two identical resistors with resistance \(R = 5\,\Omega\) and an inductance with \(L = 2\,\text{mH}\). An ideal battery of 15 V is connected in the circuit. What will be the current through the battery long after the switch is closed ?

The position vector of the centre of mass \(\vec{r}_{cm}\) of an asymmetric uniform bar of negligible area of crosssection as shown in figure is :

The galvanometer deflection, when key \(K_1\) is closed but \(K_2\) is open, equals \(\theta_0\) (see figure). On closing \(K_2\) also and adjusting \(R_2\) to \(5\,\Omega\), the deflection in galvanometer becomes \(\frac{\theta_0}{5}\). The resistance of the galvanometer is, then, given by [Neglect the internal resistance of battery] :

Two light identical springs of spring constant k are attached horizontally at the two ends of a uniform horizontal rod AB of length \(\ell\) and mass m. The rod is pivoted at its centre 'O' and can rotate freely in horizontal plane. The other ends of the two springs are fixed to rigid supports as shown in figure. The rod is gently pushed through a small angle and released. The frequency of resulting oscillation is :

A point source of light, S is placed at distance L in front of the centre of plane mirror of width d which is hanging vertically on a wall. A man walks in front of the mirror along a line parallel to the mirror, at a distance 2L as shown below. The distance over which the man can see the image of the light source in the mirror is

The least count of the main scale of a screw gauge is 1 mm. The minimum number of divisions on its circular scale required to measure 5 \(\mu\)m diameter of a wire is :

If a variable line, \(3x + 4y - \lambda = 0\) is such that the two circles \(x^2 + y^2 - 2x - 2y + 1 = 0\) and \(x^2 + y^2 - 18x - 2y + 78 = 0\) are on its opposite sides, then the set of all values of \(\lambda\) is the interval :

Let \(S_k = \frac{1 + 2 + 3 + \dots + k}{k}\). If \(S_1^2 + S_2^2 + \dots + S_{10}^2 = \frac{5}{12}A\), then A is equal to :

The perpendicular distance from the origin to the plane containing the two lines, \(\frac{x+2}{3} = \frac{y-2}{5} = \frac{z+5}{7}\) and \(\frac{x-1}{1} = \frac{y-4}{4} = \frac{z+4}{7}\), is :

Let \(C_1\) and \(C_2\) be the centres of the circles \(x^2 + y^2 - 2x - 2y - 2 = 0\) and \(x^2 + y^2 - 6x - 6y + 14 = 0\) respectively. If P and Q are the points of intersection of these circles, then the area (in sq. units) of the quadrilateral \(PC_1QC_2\) is :

The sum of the distinct real values of \(\mu\), for which the vectors, \(\mu\hat{i} + \hat{j} + \hat{k},\ \hat{i} + \mu\hat{j} + \hat{k},\ \hat{i} + \hat{j} + \mu\hat{k}\) are co-planar, is :

There is a uniform spherically symmetric surface charge density at a distance \(R_0\) from the origin. The charge distribution is initially at rest and starts expanding because of mutual repulsion. The figure that represents best the speed \(V(R(t))\) of the distribution as a function of its instantaneous radius \(R(t)\) is :