Practice Questions

Q30.A tunning fork of frequency 480 Hz is used in an experiment for measuring speed of sound (v) in air by resonance tube method. Resonance is observed to occur at two successive lengths of the air column, l1 = 30 cm and l2 = 70 cm. Then, ν is equal to: (1) 384 m s−1 (2) 332 m s−1 (3) 338 m s−1 (4) 379 m s−1 Q31. 25 g of an unknown hydrocarbon upon burnig produces 88 g of CO2 and 9g of H2O. This unknown hydrocarbon contains: (1) 24 g of carbon and 1 g of hydrogen (2) 18 g of carbon annd 7 g of hydrogen (3) 22 g of carbon and 3 g of hydrogen (4) 20 g carbon and 5 g of hydrogen

Q30.A Sample of radioactive material 𝐴, that has an activity of 10 𝑚 Ci 1 𝐶𝑖= 3.7 × 1010 decays s-1, has twice the number of nuclei as another sample of a different radioactive material 𝐵 which has an activity of 20 𝑚 Ci. The correct choices for half-lives of 𝐴 and 𝐵 would then be, respectively: (1) 5 days and 10 days (2) 10 days and 40 days (3) 20 days and 10 days (4) 20 days and 5 days JEE Main 2019 (09 Jan Shift 1) JEE Main Previous Year Paper 1

Q31.The quantum number of four electrons are given below: I . n = 4, l = 2, ml = – 2, ms = – 1 / 2 II . n = 3, l = 2, ml = 1, ms = + 1 / 2 III . n = 4, l = 1, ml = 0, ms = + 1 / 2 IV . n = 3, l = 1, ml = 1, ms = – 1 / 2 The correct order of their increasing energies will be: (1) I < III < II < IV (2) IV < II < III < I (3) I < II < III < II (4) IV < III < II < I

Q31.A 10mg effervescent tablet containing sodium bicarbonate and oxalic acid releases 0.25 mL of CO2 at T = 298.15 K and P = 1 bar. If molar volume of CO2 is 25.0 L under such condition, what is the percentage of sodium bicarbonate in each tablet? [Molar mass of NaHCO3 = 84 g mol−1] (1) 0.84 (2) 33.6 (3) 16.8 (4) 8.4

Q31.Which of the graphs shown below does not represent the relationship between incident light and the electron ejected from metal surface? JEE Main 2019 (10 Jan Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)

Q31.The 71st electron of an element X with an atomic number of 71 enters the orbital: (1) 5d (2) 4f (3) 6p (4) 6s

Q31.What is the work function of the metal if the light of wavelength 4000 A generates photoelectrons of velocity 6 × 105 ms−1 from it? (Mass of electron = 9 × 10−31 kg, velocity of light = 3 × 108 ms−1 , Planck's constant = 6 .626 ×10−34 Js, Charge of electron = 6 .626 ×10−34 Js) (1) 0 .9 eV (2) 4 .0 eV (3) 3 .1 eV (4) 2 .1 eV

Q31.For emission line of atomic hydrogen from ni = 8 to nf = n, the plot of wave number -v against n2 will be: (The Rydberg constant, RH is in wave number unit) (1) Linear with slope -RH (2) Non linear (3) Linear with slope RH (4) Linear with intercept -RH

Q31.The minimum amount of O2g consumed per gram of reactant is for the reaction: (Given atomic mass: Fe = 56, O = 16, Mg = 24, P = 31, C = 12, H = 1 ) (1) P4s + 5O2g →P4O10s (2) 2 Mgs + O2g →2MgOs (3) 4Fes + 3O2g →2Fe2O3s (4) C3H8g + 5O2g →3CO2g + 4H2O ( l )

Q31.For the following reaction, the mass of water produced from 445 g of C57H110O6 is: 2 C57H110O6(s) + 163O2(g) →114 CO2(g) + 110H2O(l) (1) 490 g (2) 890 g (3) 445 g (4) 495 g

Q31.At 300 K and 1 atmospheric pressure, 10 mL of a hydrocarbon required 55 mL of O2 for complete combustion, and 40 mL of CO2 is formed. The formula of the hydrocarbon is: (1) C4H8 (2) C4H10 (3) C4H6 (4) C4H7Cl

Q31.For a reaction, N2(g) + 3H2(g) ⟶2NH3(g), identify di-hydrogen (H2) as a limiting reagent in the following reaction mixtures. (1) 28 g of N2 + 6 g of H2 (2) 35 g of N2 + 8 g of H2 (3) 56 g of N2 + 10 g of H2 (4) 14 g of N2 + 4 g of H2

Q32.Which one of the following about an electron occupying the 1s orbital in a hydrogen atom is incorrect? (The Bohr radius is represented by a0 ). (1) The total energy of the electron is maximum when it is at a distance a0 from the nucleus. (2) The electron can be found at a distance 2a0 from the nucleus. (3) The probability density of finding the electron is maximum at the nucleus. (4) The magnitude of the potential energy is double that of its kinetic energy on an average.

Q32.Heat treatment of muscular pain involves radiation of wavelength of about 900nm. Which spectral line of H atom is suitable for this purpose? [RH = 1 × 105 cm−1 ⋅h = 6.6 × 10−34Js, c = 3 × 108 ms−1] (1) Paschen, ∞→3 (2) Paschen, 5 →3 (3) Balmer, ∞→2 (4) Lyman, ∞→1

Q32.Which of the following combination of statements is true regarding the interpretation of the atomic orbitals? (A) An electron in an orbital of high angular momentum stays away from the nucleus than an electron in the orbital of lower angular momentum. JEE Main 2019 (09 Jan Shift 2) JEE Main Previous Year Paper (B) For a given value of the principal quantum number, the size of the orbit is inversely proportional to the azimuthal quantum number. (C) According to wave mechanics, the ground state angular momentum is equal to 2πh . (D) The plot of ψ Vs r for various azimuthal quantum numbers, shows peak shifting towards higher r value. (1) (B), (C) (2) (A), (B) (3) (A), (C) (4) (A), (D)

Q32.The graph between |ψ|2 and r (radical distance) is shown below. This represents: (1) 3s orbital (2) 2p orbital (3) 2s orbital (4) 1s orbital

Q32.The ground state energy of a hydrogen atom is −13 .6 eV. The energy of second excited state of He+ ion in eV is: (1) −27.2 (2) −6.04 (3) −3.4 (4) −54.4

Q32.The ratio of the shortest wavelength of two spectral series of hydrogen spectrum is found to be about 9. The spectral series are: (1) Paschen and Pfund (2) Balmer and Brackett (3) Lyman and Paschen (4) Brackett and Pfund

Q32.The de Broglie wavelength (λ) associated with a photoelectron varies with the frequency (v) of the incident radiation as, [v0 is threshold frequency]: 1 (1) λ ∝ 1 (2) λ ∝ 1 (v−v0) 4 (v−v0) (3) λ ∝ 1 3 (4) λ ∝ 1 1 (v−v0) 2 (v−v0) 2

Q32.If the de Broglie wavelength of the electron in nth Bohr orbit in a hydrogenic atom is equal to 1.5πa0 (a0 is Bohr radius ), then the value of nz is: (1) 1.50 (2) 1.0 (3) 0.4 (4) 0.75

Q32.For any given series of spectral lines of atomic hydrogen, let Δ−v = −v max −−v min be the difference in maximum and minimum wave number in cm−1 . The ratio Δ−v Lyman/Δ−v Balmar is (1) 5 : 4 (2) 27 : 5 (3) 4 : 1 (4) 9 : 4

Q33.Among the following species, the diamagnetic molecule is: (1) CO (2) B2 (3) O2 (4) NO

Q33.Given: On the basis of data given above, predict which of the following gases shows the least adsorption on a definite amount of charcoal? (1) CH4 (2) CO2 (3) SO2 (4) H2

Q33.Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas? (Assume non- expansion work is zero) (1) Isochoric process : (2) Isochoric process : (3) Cyclic process : (4) Adiabatic process : ΔU = q q = – w q = – w ΔU = - w

Q33.Two pi and half sigma bonds are present in: (1) O−2 (2) N 2+ (3) N2 (4) O2