Recent questions in JEEMAIN and NEET

Which of the following is the correct order of decreasing $S_N2$ reactivity ? (X = a halogen)

asked Nov 29, 2018 by pady_1

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Which one of the following conformations of cyclohexane is chiral ?

asked Nov 29, 2018 by pady_1

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A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room ?

asked Nov 29, 2018 by pady_1

1 answer

In a saturated solution of the sparingly soluble strong electrolyte $AgIO_3$ (Molecular mass = 283) the equilibrium which sets in is $AgIO_3(s) \rightleftharpoons Ag^+ (aq) + IO_3^- (ag)$ if the solubility product constant $K_{sp}$ of $AgIO_3$ at a given temperature is $1.0 \times 10^{-8}$, what is the mass of $AgIO_3$ contained in 100 mL of its saturated solution ?

asked Nov 29, 2018 by pady_1

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Assuming that water vapour is an ideal gas, the internal energy change ($\Delta U$) when 1 mole of water is vapourised at 1 bar pressure and $100^{\circ}C$, (Given : molar enthalpy of vaporisation of water at 1 bar and 373 K = 41 kJ mol$^{-1}$ and R = 8.3 J mol$^{-1}$ K$^{-1}$ ) will be :

asked Nov 29, 2018 by pady_1

1 answer

A 5.25% solution of a substance is isotonic with a 1.5% solution of urea (molar mass = $60 \; g\; mol^{-1}$) in the same solvent. If the densities of both the solutions are assumed to be equal to $1.0\; g\; cm^{-3}$, molar mass of the substance will be :

asked Nov 29, 2018 by pady_1

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Equal masses of methane and oxygen are mixed in an empty container at $25^{\circ}C$. The fraction of the total pressure exerted by oxygen is :

asked Nov 29, 2018 by pady_1

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The actinoids exhibit more number of oxidation states in general than the lanthanoids. This is because :

asked Nov 29, 2018 by pady_1

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In which of the following ionisation processes, the bond order has increased and the magnetic behaviour has changed ?

asked Nov 29, 2018 by pady_1

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Presence of a nitro group in a benzene ring :

asked Nov 29, 2018 by pady_1

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The reaction of toluene with $Cl_2$ in presence of $FeCl_3$ gives predominantly :

asked Nov 29, 2018 by pady_1

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In the chemical reaction, $CH_3CH_2NH_2 + CHCl_3 + 3 KOH \to$ $(A) + (B) + 3H_2O$, the compounds $(A)$ and $(B)$ are respectively :

asked Nov 29, 2018 by pady_1

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Which of the following reactions will yield, 2, 2-dibromopropane ?

asked Nov 29, 2018 by pady_1

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The secondary structure of a protein refers to :

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Which of the following molecules is expected to rotate the plane of plane-polarised light ?

asked Nov 29, 2018 by pady_1

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Which one of the following has a square planar geometry ? (At. no. Co = 27, Ni = 28, Fe = 26, Pt = 78)

asked Nov 29, 2018 by pady_1

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Identify the incorrect statement among the following :

asked Nov 29, 2018 by pady_1

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Consider the reaction, $2A + B \to products$ When concentration of B alone was doubled, the half-life did not change. When the concentration of A alone was doubled, the rate increased by two times. The unit of rate constant for this reaction is :

asked Nov 29, 2018 by pady_1

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The $pK_a$ of a weak acid (HA) is 4.5. The pOH of an aqueous buffered solution of HA in which 50% of the acid ionised is :

asked Nov 29, 2018 by pady_1

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The cell $Zn|Zn^{2+} (1M) || Cu^{2+} (1M) | Cu \; (E^{\circ} cell = 1.10 V)$, was allowed to be completely discharged at 298 K. The relative concentration of $Zn^{2+}$ to $Cu^{2+} \begin{pmatrix} \frac{[Zn^{2+}]}{[Cu^{2+}]} \end{pmatrix} $ is :

asked Nov 29, 2018 by pady_1

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The energies of activation for forward and reverse reactions for $A_2 + B_2 \leftrightharpoons 2AB$ are $180\; kJ\;mol^{-1}$ and $200 \; kJ \;mol^{-1}$ respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by $100\; kJ\; mol^{-1}$. The enthalpy change of the reaction ($A_2 + B_2 \to 2AB$) in the presence of catalyst will be (in $kJ\;mol^{-1}$) :

asked Nov 29, 2018 by pady_1

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A particle of mass m executes simple harmonic motion with amplitude $a$ and frequency $v$. The average kinetic energy during its motion from the position of equilibrium to the end is :

asked Nov 29, 2018 by pady_1

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When a system is taken from state $i$ to state $f$ along the path $iaf$, it is found that $Q=50 \;cal$ and $W=20\; cal$. Along the path $ibf$ Q = 36 cal. W along the path $ibf$ is :

asked Nov 29, 2018 by pady_1

1 answer

Two springs, of force constants $k_1$ and $k_2$ are connected to a mass m as shown. The frequency of oscillation of the mass is $f$. If both $k_1$ and $k_2$ are made four times their original values, the frequency of oscillation becomes :

asked Nov 29, 2018 by pady_1

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In a Young's double slit experiment the intensity at a point where the path difference is $\frac{\lambda}{6}$ ($\lambda$ being the wavelength of the light used) is $I$. If $I_0$ denotes the maximum intensity, $I/ I_0$ is equal to :

asked Nov 29, 2018 by pady_1

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A particle is projected at $60^{\circ}$ to the horizontal with a kinetic energy $K$. The kinetic energy at the highest point is :

asked Nov 29, 2018 by pady_1

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A 2 kg block slides on a horizontal floor with a speed of 4 m/s. It strikes a uncompressed spring, and compresses it till the block is motionless. The kinetic friction force is 15 N and spring constant is 10,000 N/m. The spring compresses by :

asked Nov 29, 2018 by pady_1

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Angular momentum of the particle rotating with a central force is constant due to :

asked Nov 29, 2018 by pady_1

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A round uniform body of radius R, mass M and moment of inertia I, rolls down (without slipping) an inclined plane making an angle $\theta$ with the horizontal.Then its acceleration is :

asked Nov 29, 2018 by pady_1

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A circular disc of radius $R$ is removed from a bigger circular disc of radius $2R$, such that the circumference of the discs coincide. The centre of mass of the new disc is $\frac{\alpha}{R}$ from the centre of the bigger disc. The value of $\alpha$ is :

asked Nov 29, 2018 by pady_1

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If $g_{_E}$ and $g_{_M}$ are the accelerations due to gravity on the surfaces of the earth and the moon respectively and if Millikan's oil drop experiment could be performed on the two surfaces, one will find the ratio $\frac{electronic \;charge \;on \;the \;moon}{electronic \;charge \;on \;the \;earth} $to be :

asked Nov 29, 2018 by pady_1

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A parallel plate condenser with a dielectric of dielectric constant $K$ between the plates has a capacity $C$ and is charged to a potential $V$ volts. The dielectric slab is slowly removed from between the plates and then reinserted. The network done by the system in this process is:

asked Nov 29, 2018 by pady_1

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The resistance of a wire is $5 \Omega$ at $50^{\circ}C$ and $6 \Omega$ at $100^{\circ} C$. The resistance of the wire at $0^{\circ} C$ will be :

asked Nov 29, 2018 by pady_1

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Two identical conducting wires AOB and COD are placed at right angles to each other. The wire AOB carries an electric current $I_1$ and COD carries a current $I_2$. The magnetic field on a point lying at a distance d from O, in a direction perpendicular to the plane of the wires AOB and COD, will be given by :

asked Nov 29, 2018 by pady_1

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A charged particle moves through a magnetic field perpendicular to its direction. Then :

asked Nov 29, 2018 by pady_1

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If $C_P$ and $C_V$ denote the specific heats of nitrgen per unit mass at constant pressure and constant volume respectively, then :

asked Nov 29, 2018 by pady_1

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A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of :

asked Nov 29, 2018 by pady_1

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One end of a thermally insulated rod is kept at a temperature $T_1$ and the other at $T_2$. The rod is composed of two section of length $l_1$ and $l_2$ and thermal conductivities $K_1$ and $K_2$ respectively. The temperature at the interface of the two sections is

asked Nov 29, 2018 by pady_1

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Two lenses of power -15D and +5D are in contact with each other. The focal length of the combination is :

asked Nov 29, 2018 by pady_1

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A block of mass m is connected to another block of mass M by a spring (massless) of spring constant k. The blocks are kept on a smooth horizontal plane. Initially the blocks are at rest and the spring is unstretched. Then a constant force F starts acting on the block of mass M to pull it. Find the force on the block of mass m.

asked Nov 29, 2018 by pady_1

1 answer

Which of the following transitions in hydrogen atoms emit photons of highest frequency ?

asked Nov 29, 2018 by pady_1

0 answers

The potential at a point $x$ (measured in $\mu m$) due to some charges situated on the $x$-axis is given by : $V(x) = 20/(x^2 - 4)$ volt The electric field $E$ at $x=4 \mu m$ is given by :

asked Nov 29, 2018 by pady_1

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A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields $\overrightarrow{E}$ and $\overrightarrow{B}$ with a velocity $\overrightarrow{v}$ perpendicular to both $\overrightarrow{E}$ and $\overrightarrow{B}$, and comes out without any change in magnitude or direction of $\overrightarrow{v}$. Then :

asked Nov 29, 2018 by pady_1

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Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate ?

asked Nov 29, 2018 by pady_1

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A Carnot engine, having an efficiency of $\eta = 1/10$ as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is :

asked Nov 29, 2018 by pady_1

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The half-life period of a radioactive element X is same as the mean life time of another radioactive element Y. Initially they have the same number of atoms. Then :

asked Nov 29, 2018 by pady_1

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Charges are placed on the vertices of a square as shown. Let $\overrightarrow{E}$ be the electric field and $V$ the potential at the centre. If the charges on A and B are interchanged with those on D and C respectively, then :

asked Nov 29, 2018 by pady_1

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A point mass oscillates along the $x$-axis according to the law $x=x_0 \cos (\omega t - \pi/4)$. If the acceleration of the particle is written as : $a = A \cos (\omega t + \delta)$, then :

asked Nov 29, 2018 by pady_1

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For the given uniform square lamina ABCD, whose centre is O :

asked Nov 29, 2018 by pady_1

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The velocity of a particle is $\nu = \nu_{_0} + gt = ft^2$. If its position is $x=0$ at $t=0$, then its displacement after unit time $(t=1)$ is :

asked Nov 29, 2018 by pady_1

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