List of top Questions asked in JEE Main- 2019

A solution of sodium sulfate contains $92\, g$ of ${Na^{+}}$ ions per kilogram of water. The molality of ${Na^{+}}$ ions in that solution in ${mol \; kg^{-1}}$ is:

The transition element that has lowest enthalpy of atomisation, is :

1 g of non-volatile non-electrolyte solute is dissolved in 100g of two different solvents A and B whose ebullioscopic constants are in the ratio of 1 : 5. The ratio of the elevation in their boiling points, $\frac{\Delta T_b(A)}{\Delta T_b (B)}$, is:

Aluminium is usually found in $+3$ oxidation stagte. In contarast, thallium exists in $+1$ and $+3$ oxidation states. This is due to :

An example of solid sol is :

The correct order of hydration enthalpies of alkali metal ions is -

The correct statement regarding the given Ellingham diagram is:

Glucose and Galactose are having identical configuration in all the positions except position.

Which is the most suitable reagent for the following transformation ?

Which of the following compounds is not aromatic ?

A plano-convex lens (focal length $f_2$, refractive index $\mu_2$, radius of curvature $R$) fits exactly into a plano-concave lens (focal length $f_1$, refractive index $\mu_2$, radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be :

Voltage rating of a parallel plate capacitor is $500\,V$. Its dielectric can withstand a maximum electric field of $10^6$ V/m. The plate area is $10^{-4} \; m^2$. What is the dielectric constant is the capacitance is $15\, pF$ ? (given $\in_0 = 8.86 \times 10^{-12} C^2 / Nm^2$)

An alpha-particle of mass m suffers 1-dimensional elastic coolision with a nucleus at rest of unknown mass. It is scattered directly backwards losing, $64\%$ of its initial kinetic energy. The mass of the nucleus is :

The magnitude of torque on a particle of mass $1\,kg$ is $2.5\, Nm$ about the origin. If the force acting on it is $1\, N$, and the distance of the particle from the origin is $5\,m$, the angle between the force and the position vector is (in radians) :

A load of mass $M\, kg$ is suspended from a steel wire of length $2\, m$ and radius $1.0\, mm$ in Searle's apparatus experiment. The increase in length produced in the wire is $4.0\, mm$. Now the load is fully immersed in a liquid of relative density $2$. The relative density of the material of load is $8$. The new value of increase in length of the steel wire is :

A $10\, m$ long horizontal wire extends from North East to South West. It is falling with a speed of $5.0\,ms^{-1}$, at right angles to the horizontal component of the earth's magnetic field, of $0.3 \times 10^{-4}\,Wb/m^2$. The value of the induced emf in wire is :

A straight rod of length $L$ extends from $x = a$ to $x = L + a$. The gravitational force is exerts on a point mass $'m'$ at $x = 0$, if the mass per unit length of the rod is $A + Bx^2$, is given by:

A particle starts from origin $O$ from rest and moves with a uniform acceleration along the positive $x$-axis. Identify all figures that correctly represent the motion qualitatively. (a = acceleration, v = velocity, x = displacement, t = time)

An electron, moving along the x-axis with an initial energy of $100\, eV$, enters a region of magnetic field $\vec{B} \, = (1.5 \times 10^{-3} T) \hat{k}$ at $S$ (See figure). The field extends between $x = 0$ and $x = 2\, cm$. The electron is detected at the point $Q$ on a screen placed $8\, cm$ away from the point $S$. The distance $d$ between $P$ and $Q$ (on the screen) is : (electron's charge = $1.6 \times 10^{-19}C.$ mass of electron = $9.1 \times 10^{-31}kg)$

Two radioactive materials $A$ and $B$ have decay constants $10 \lambda$ and $\lambda$, respectively. It initially they have the same number of nuclei, then the ratio of the number of nuclei of $A$ to that of $B$ will be $1/e$ after a time :

One plano-convex and one plano-concave lens of same radius of curvature $'R'$ but of different materials are joined side by side as shown in the figure. If the refractive index of the material of $1$ is $\mu_1$ and that of $2$ is $\mu_2$, then the focal length of the combination is :

A vertical closed cylinder is separated into two parts by a frictionless piston of mass $m$ and of negligible thickness. The piston is free to move along the length of the cylinder. The length of the cylinder above the piston is $\ell_1$, and that below the piston is $\ell_2$ , such that $\ell_1$>$\ell_2$. Each part of the cylinder contains $n$ moles of an ideal gas at equal temperature $T$. If the piston is stationary, its mass, $m$, will be given by : (R is universal gas constant and $g$ is the acceleration due to gravity)

Two identical spherical balls of mass $M$ and radius $R$ each are stuck on two ends of a rod of length $2R$ and mass $M$ (see figure). The moment of inertia of the system about the axis passing perpendicularly through the centre of the rod is :

A message signal of frequency $100\, MHz$ and peak voltage $100\, V$ is used to execute amplitude modulation on a carrier wave of frequency $300\, GHz$ and peak voltage $400\, V$. The modulation index and difference between the two side band frequencies are :

In the given circuit diagram, the currents, $I_1 = 0.3\,A, I_4 = 0.8\, A$ and $I_5 = 0.4\, A$, are flowing as shown. The currents $I_2,I_3$ and $I_6$,respectively, are :