Recent questions in JEEMAIN PAST PAPERS

Using MO theory predict which of the following species has the shortest bond length ?

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Which one of the following reactions of Xenon compounds is not feasible ?

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Solid $Ba(NO_3)_2$ is gradually dissolved in a $1.0 \times 10^{-4} M\; Na_2CO_3$ solution. At what concentration of $Ba^{2+}$ will a precipitate begin to form ? ($K_{sp}$ for $BaCO_3 = 5.1 \times 10^{-9} $ ).

asked Nov 29, 2018 by pady_1

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Which of the following has as optical isomer ?

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Copper crystallizes in fcc wih a unit cell length of 361 pm. What is the radius of copper atom ?

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On the basis of the following thermochemical data : $(\Delta f G^{\circ} H^+_{(aq)} = 0 ) $ $ H_2O (\ell) \to H^+ (aq) + OH^- (aq); \Delta H= 57.32 \; kJ$ $H_2 (g) + \frac{1}{2} O_2 (g) \to H_2O (\ell); \Delta H = -286.20 \; kJ$ The value of enthalpy of formation of $OH^-$ ion at $25^{\circ}C$ is :

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Given : $E^o_{Fe^{3+}/Fe} = - 0.036V,$ $E^o_{Fe^{2+}/Fe} = -0.439\; V$. The value of standard electrode potential for the change, $Fe^{3+}_{(aq)} + e^- \to Fe^{2+} (aq)$ will be :

asked Nov 29, 2018 by pady_1

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The half life period of a first order chemical reaction is 6.93 minutes. The time required for the completion of 99% of the chemical reaction will be (log 2 = 0.301) :

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Two liquid X and Y form an ideal solution. At 300 K, vapour pressure of the solution containing 1 mol of X and 3 mol of Y is 550 mm Hg. At the same temperature, if 1 mol of Y is further added to this solution, vapour pressure of the solution increases by 10 mm Hg. Vapour pressure (in mm Hg) of X and Y in their pure states will be, respectively :

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In a fuel cell methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is $CH_3OH (\ell) + \frac{3}{2} O_2 (g) \to CO_2 (g) + 2H_2O (\ell)$ at 298 K standard Gibb's energies of formation for $CH_3OH (\ell), H_2O (\ell) $ and $CO_2 (g)$ are $-166.2, -237.2 $ and $-394.4$ $kJ\; mol^{-1}$ respectively. If standard enthalpy of combustion of methanol is $-726\; kJ\; mol^{-1}$, efficiency of the fuel cell will be

asked Nov 29, 2018 by pady_1

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In an atom, an electron is moving with a speed of 600 m/s with an accuracy of $0.005 \%$. Certainity with which the position of the electron can be located is ($h = 6.6 \times 10^{-34} \; kg \; m^2\; s^{-1}$, mass of electron, $e_m = 9.1 \times 10^{-31} kg$)

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Which of the following on heating with aqueous KOH, produces acetaldehyde ?

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Which of the following statement is incorrect regarding physissorptions ?

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The major product obtained on interaction of phenol with sodium hydroxide and carbon dioxide is :

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In which of the following arrangements, the sequence is not strictly according to the property written against it ?

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The alkene that exhibits geometrical isomerism is :

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Arrange the carbanions, $(CH_3)_3 \overline{C}, \;\overline{C}Cl_3, (CH_3)_2 \overline{C}H, \;C_6H_5 \overline{C}H_2,$ in order of thier decreasing stability :

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A liquid was mixed with ethanol and a drop of concentrated $H_2SO_4$ was added. A compound with a fruity smell was formed. The liquid was :

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Knowing that the Chemistry of lanthanoids (Ln) is dominated by its $+3$ oxidation state, which of the following statements is incorrect ?

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The net work done on the gas in the cycle ABCDA is

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The work done on the gas in taking it from D to A is

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Assuming the gas to be ideal the work done on the gas in taking it from A to B is

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An inductor of inductance L =400 mH and resistors of resistances $R_1 = 2 \Omega$ and $R_2 = 2 \Omega$ are connected to a battery of emf 12V as shown in the figure. The internal resistance of the battery is negligible. The switch S is closed at t = 0. The potential drop across L as a function of time is

asked Nov 29, 2018 by pady_1

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In an experiment the angles are required to be measured using an instrument. 29 divisions of the main scale exactly coincide with the 30 divisions of the vernier scale. If the smallest division of the main scale is half-a-degree ($=0.5^{\circ}$), then the least count of the instrument is

asked Nov 29, 2018 by pady_1

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Two wires are made of the same material and have the same volume. However wire 1 has cross-sectional area A and wire-2 has cross-sectional area 3A. If the length of wire 1 increases by $\Delta$ x on applying force F, how much force is needed to stretch wire 2 by the same amount ?

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The height at which the acceleration due to gravity becomes $\frac{g}{9}$ (where g = the acceleration due to gravity on the surace of the earth) in terms of R, the radius of the earth is

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Three sound waves of equal amplitudes has frequencies $(v-1), v, (v+1)$. They superpose to give beats. The number of beats produced per second will be

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A transparent solid cylindrical rod has a refractive index of $\frac{2}{\sqrt{3}}$. It is surrounded by air. A light ray is incident at the mid point of one end of the rod as shown in the figure. The incident angle $\theta$ for which the light ray grazes along the wall of the rod is

asked Nov 29, 2018 by pady_1

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A long metallic bar is carrying heat from one of its end to the other end under steady-state. The variation of temperature $\theta$ along the length x of the bar from its hot end is best described by which of the following figure :

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A charge Q is placed at each of the opposite corners of a square. A charge q is placed at each of the other two corners. If the net electrical force on Q is zero, tthen the Q/q equals

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Consider a rubber ball freely falling from a height h = 4.9 m onto a horizontal elastic plate. Assume that the duration of collision is negligible and the collision with the plate is totally elastic. Then the velocity as a function of time the height as function of time will be

asked Nov 29, 2018 by pady_1

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A motor cycle starts from rest and acceleration along a straight path at $2\; m/s^2$. At the starting point of the motor cycle there is a stationary electric sire. How far has the motor cycle gone when the driver hears the frequency of the siren at 94% of its value when the motor cycle was at rest ? (speed of sound = 330 $ms^{-1}$ )$

asked Nov 29, 2018 by pady_1

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A particle has an initial velocity $3 \hat{i} + 4 \hat{j}$ and an acceleration of $0.4 \hat{i} + 0.3 \hat{j}$. Its speed after 10 s is

asked Nov 29, 2018 by pady_1

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The surface of a metal is illuminated with the light of 400 nm. The kinetic energy of the ejected photoelectrons was found to be 1.68 eV. The work function of the metal is (hc = 1240 eV nm)

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Two points P and Q are maintained at the potentials of 10V and -4V respectively. The work done in moving 100 electrons from P to Q is

asked Nov 29, 2018 by pady_1

1 answer

A mixture of light, consisting of wavelength 590 nm and an unknown wavelength , illuminates Young's double slit and gives rise to two overlapping interference patterns on the screen. The central maximum of both lights coincide. Further, it is observed that the third bright fringe of known light coincides with the $4^{th}$ bright fringe of the unknown light. From this data, the wavelength of the unknown light is

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Due to the presence of the current I, at the origin

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The magnitude of the magnetic field (B) due to loop ABCD at the origin (O) is

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This question contains Statement-1 and Statement-2. Of the four choices given after the statements, choose the one that best describes the two statements. Statement-1 : The temperature dependence of resistance is usually given as $R = R_o(1+ \alpha \Delta t)$. The resistance of a wire changes from $100 \Omega$ to $150 \Omega$ when its temperature is increased from $27^{\circ}C$ to $227^{\circ}C$. This implies that $\alpha = 2.5 \times 10^{-3} /^{\circ} C$. Statement 2 : $R = R_i (1 + \alpha \Delta T)$ is valid only when the change in the temperature $\Delta T$ is small and $\Delta R= (R-R_o) < < R_o$.

asked Nov 29, 2018 by pady_1

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One kg of a diatomic gas is at a pressure of $8 \times 10^4\;N/m^2$. The density of the gas is $4\; kg/m^{3}$. What is the energy of the gas due to its thermal motion ?

asked Nov 29, 2018 by pady_1

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The transition from the state $n=4$ to $n=3$ in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from

asked Nov 29, 2018 by pady_1

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Let $P(r) = \frac{Q}{\pi R^4} r$ be the charge density distribution for a solid sphere of radius R and total charge Q for a point 'p' inside the sphere at distance $r_1$ from the centre of the sphere, the magnitude of electric field is

asked Nov 29, 2018 by pady_1

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A thin uniform rod of length $\ell$ and mass $m$ is swinging freely about a horizontal axis passing through its end. Its maximum angular speed is $\omega$. Its centre of mass rises to a maximum height of

asked Nov 29, 2018 by pady_1

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In an optics experiment, with the position of the object fixed, a student varies the position of a convex lens and for each position, the screen is adjusted to get a clear image of the object. A graph between the object distance $u$ and the image distance $v$, from the lens, is plotted using the same scale for the two axes. A straight line passing through the origin and making an angle of $45^{\circ}$ with the $x$-axis meets the experimental curve at $P$. The coordinates of $P$ will be

asked Nov 29, 2018 by pady_1

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If $x, v$ and a denote the displacement, the velocity and the acceleration of a particle executing simple harmonic motion of time period T, then, which of the following does not change with time ?

asked Nov 29, 2018 by pady_1

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The logic circuit below has the input waveforms 'A' and 'B' as shown. Pick out the correct output waveform.

asked Nov 29, 2018 by pady_1

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A p-n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit.

asked Nov 29, 2018 by pady_1

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The above is a plot of binding energy per nucleon $E_b$, against the nuclear mass M; A, B, C, D, E, F correspond to different nuclei. Consider four reactions : (i) $ A + B \to C + \varepsilon \; \; \; \;$ (ii) $ C \to A + B + \varepsilon \; \; \; \;$ (iii) $D+ E \to F + \varepsilon \; and \; \; \; \; $ (iv) $ F \to D + E + \varepsilon$ where $\varepsilon$ is the energy released ? In which reactions is $\varepsilon$ positive ?

asked Nov 29, 2018 by pady_1

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This question contains Statement - 1 and Statement - 2. Of the four choices given after the statements, choose the one that best describes the two statements. Statement - 1 : For a charged particle moving from point P to point Q, the net work done by an electrostatic field on the particle is independent of the path connecting point P to point Q. Statement -2 : The net work done by a conservative force on an object moving along a closed loop is zero.

asked Nov 29, 2018 by pady_1

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In the following sequence of reactions, the alkene affords the compound ‘B’ $CH_3CH = CHCH_3 \xrightarrow{O_3} A \xrightarrow[\text{Zn}]{\text{$H_2O$}} B$ The compound is :

asked Nov 29, 2018 by pady_1

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