Explore topic-wise InterviewSolutions in .

Correct answer is (b) 2

To ELABORATE: Total number of nodes INCLUDE angular and radial nodes. Angular nodes and radial nodes are given by the formula N – L -1 and l RESPECTIVELY. So the total number of nodes are n – l -1 + l = n – 1. For 3d orbit, “n” is 3, so total number nodes is 3 – 1 = 2.

The correct CHOICE is (c) 0.176 X 10^-34

To elaborate: Speed’s uncertainty is 10 x 5/100 = 0.5 m/s. We have Heisenberg’s PRINCIPLE of uncertainty i.e. Δx. Δp ≥ h/4π. Δx = h/2mπ. Therefore uncertainty in position = 6.626 x 10^-34 Js/12 x 3.1416 = 0.176 x 10^-34.

The correct CHOICE is (a) True

To elaborate: Heisenberg’s principle of uncertainty STATES that the product of relative momentum and VELOCITIES is equal to greater than the h/4π, where is “h” is the Planck’s constant and is equal to 6.626 x 10^-34 Js. HENCE the above statement is true.

The correct choice is (d) 3.313 x 10^15 m/s

For explanation I would SAY: We know that the mass of an ELECTRON is 9.1 x 10^-31 kg. Given that the kinetic ENERGY of an electron is 5J. K.E = mv^2/2 and by SUBSTITUTING we get v = √1.098 x 10^31 m/s = 3.313 x 10^15m/s.

The correct option is (a) √h/4π

The BEST I can EXPLAIN: As we know, Heisenberg’s PRINCIPLE of uncertainty states that Δx. Δp ≥ h/4π, X is position, P is momentum and “h” is the Planck’s constant. Δx = Δp; Δx. Δx = h/4π; Δx = √h/4π

Right ANSWER is (a) True

For EXPLANATION: Yes, chemical properties of an atom is dependent on a NUMBER of electrons in that particular atom, which in TURN is decided by the number of protons PRESENT in that atom. The number of neutrons has only a small effect on this.

Correct choice is (b) False

Explanation: When an electron jumps from n^th orbit to 1ST orbit, provided that n = 1, 2, 3, etc, it emits radion in the ultraviolet region. As per the spectral LINES of the HYDROGEN, when an electron jumps from n^th orbit to 2^nd orbit, it’s in Balmer SERIES (provided that n = 3, 4, 5….). For Balmer series, the electron emits WAVES in the visible region.

Right choice is (a) 1.758820 × 10^11 C kg^-1

Easy explanation: A British physicist J. J. Thomson carried out experiments and observed the DEFLECTIONS made by ELECTRONS in an electric or magnetic field. He finally CALCULATED ELECTRON’s charge to mass ratio as e/me = 1.758820 × 10^11 C kg^-1. The units of charge and mass are in coulomb and kg respectively.

Right answer is (C) 20, 17, 17

To explain I would SAY: An atom is written in the symbol ZXA. By COMPARING it to 17Cl^37, we get a number of protons as 17 and mass number as 37. Mass number – proton number = neutron number. Number of neutrons is 37 – 17 = 20. No. of protons = No. of electrons = 17.

Correct answer is (a) Radioactivity

The best I can explain: HENRI Becquerel discovered that ELEMENTS emit radiation and termed this phenomenon as radioactivity. Later Curie on RESEARCH found out about α-rays, β-rays and γ-rays. Later RUTHERFORD concluded that α particles are helium nuclei.

The correct answer is (B) J. J. Thomson

To explain: Thomson proposed a model of the atom, in which electrons are embedded to make it as the stable electrostatic arrangement and such that positive charge is equally distributed around a sphere. MASS is assumed to be equally distributed. So. it has different NAMES like plum PUDDING, watermelon and RAISIN pudding model.

Correct option is (b) 2 x 10^-34 m

The explanation is: Louis DE Brogie gave the realation between MOMENTUM and WAVELENGTH as λ = H/p. Here h is Planck’s constant, whose VALUE is 6.626 x 10^-34 J/s. Wavelength = h/mv = 2 x 10^-34 m (momentum p = mass m x velocity v).

Right choice is (b) False

The best explanation: Neutrally charged PARTICLES are known as neutrons, WHEREAS positively charged particles are protons. When Beryllium is BOMBARDED by alpha particles, neutrons were DISCOVERED by Chadwick. Their mass is a BIT greater than that of protons.

The correct CHOICE is (b) Dumbbell

Best explanation: The azimuthal quantum NUMBER is given by “L”. When l = 0, 1, 2 and 3, they are s-orbital, p-orbital, d-orbital and f-orbital respectively. The shapes of s-orbital, p-orbital, d-orbital, and f-orbital are Spherical, Dumbbell, Double dumbbell and Complex respectively.

The correct CHOICE is (a) True

The best I can EXPLAIN: According to Bohr’s postulate, angular momentum is quantized and this is GIVEN by the expression mevr = nh/2π. (n =1, 2, 3….).mevr is the angular momentum and h is the Planck’s constant. Movement of an electron can only be possible in orbits WHOSE angular momentum is the integral multiple of h/2π

Correct choice is (b) 50:153

To explain I would SAY: The atomic radius of an ATOM is given by the formula rn = 52.9n^2/Z pm, where rn is the radius of NTH orbit of an atom and Z is the atomic number of that atom. The RATIO of the atomic radius of the 5^th orbit in chlorine atom and 3^rd orbit in Helium atom is 25/17:9/2 = 50:153.

The correct choice is (b) Hund’s rule of MAXIMUM multiplicity

Easiest explanation: According to Hund’s rule of maximum multiplicity, the pairing of electrons cannot be started until each of the orbitals is singly OCCUPIED. The reason behind this is that the half-FILLED or fully filled orbitals are MUCH more stable comparatively.

Correct answer is (a) 0.67A°

The BEST explanation: Louis de Brogie GAVE the realation between momentum and wavelength as λ = h/p. Here h is Planck’s constant, whose value is 6.626 x 10^-34 J/s. Wavelength = h/mc = 6.626 x 10^-34 Js/(3.313 x 10^-34 KG x 3 x 10^8 m/s) = 0.67A°.

Correct option is (a) True

To explain I would SAY: The formula of gravitational force is given by Gm1m2/r^2. Here G is the gravitational constant, while m1 and m2 are the masses and r is the DISTANCE between m1 and m2. This THEORY is FORMULATED when classic mechanics is applied to it.

Right option is (b) –1.602176×10^-19

To explain: According to the fundamental PROPERTIES of particles, PROTONS charge is +1.602176×10^-19C. It is a subatomic PARTICLE. Rutherford discovered protons. Its elementary charge is 1. PROTON’s charge is POSITIVE.

Right option is (d) 0

To elaborate: The magnetic QUANTUM of an ORBITAL range from -( l – 1) to l – 1. Its symbol is given by m. For 2p orbital, there are 3 magnetic quantum NUMBERS namely -1, 0 and 1. For 2pz orbital its 0, taken that z is the internuclear axis.

Correct option is (C) 1.055 x 10^-24 kgm/s

Best explanation: Heisenberg’s PRINCIPLE of uncertainty states that Δx. Δp ≥ h/4π, x is position, p is momentum and “h” is the Planck’s constant and is EQUAL to 6.626 x 10^-34 JS. Relative momentum Δp = h/4πΔx = 1.055 x 10^-24 kgm/s.

Correct OPTION is (a) bright spot

The explanation: Zinc sulfide is a phosphorescent material, which has been coated on the anode. when CATHODE RAYS STRIKE on the anode, electrons HIT on the Zinc sulfide screen, hence creating a bright spot.

Right choice is (a) 4.42 x 10^-29 m

Explanation: We know E = hv through Planck’s QUANTUM Theory, where E is ENERGY, h is Planck’s CONSTANT and V is the frequency. 4.5 KJ = (6.626×10^–34 Js)(3 x 10^8m/s)/(wavelength). wavelength = 4.42 x 10^-29 m.

Correct answer is (d) 0.02645 NM

Easiest EXPLANATION: The ATOMIC radius of an atom is given by the FORMULA rn = 52.9n^2/Z pm, where rn is the radius of nth ORBIT of an atom and Z is the atomic number of that atom. For He^+, n = 1 and Z =2. Radius = 52.9(1)/2 pm = 0.02645 nm.

The correct option is (d) The thickness of the gold foil is about 100μm

To explain I would say: In this effect, a thin foil (thickness 100nm) made up of gold and coated with FLUORESCENT ZnS screen which is CIRCULAR around it. α particles MOSTLY move through the gold foil having zero DEFLECTION, a small fraction is deflected and one in twenty THOUSAND turns 180°.

Right choice is (a) Low pressure, high voltage

The EXPLANATION is: The suitable CONDITIONS of cathode ray discharge TUBE are low pressure and high pressures. Pressure can be adjusted by evacuated tubes. High voltage is applied across ELECTRODES and current starts flowing through the tube.

Right answer is (a) energy and size of the orbit

To elaborate: AMONG the four quantum NUMBERS, the principal quantum number describes the size and energy of the orbit. It is represented by the symbol “n”. For SHELLS, K, L, M, N and O, n is given by 1, 2, 3, 4 and 5.

The correct option is (B) Proton

For EXPLANATION I would SAY: In 1911, Rutherford discovered protons by performing experiments and also found out that positive charge is concentrated at centre and that it has most of the atomic mass. The name proton was first time GIVEN in the year 1920.

Correct answer is (C) electrons

For explanation I would SAY: Through cathode rays discharge tube experiments, he CONCLUDED that every substance in this UNIVERSE is made up of electrons from his experiments. He observed how cathode rays move and the charge to mass ratio of it.

Right answer is (a) Balmer

To explain I would say: As per the spectral LINES of the hydrogen, when an electron JUMPS from nth orbit to 2^nd orbit, it’s in Balmer series (provided that n = 3, 4, 5….). For Balmer series, the electron emits waves in visible region.

Correct CHOICE is (a) 1838 times of electron’s mass

Explanation: The mass of an electron is 0.00054 U. The mass of a proton is 1.00727 u. The mass of a NEUTRON is 1.00867 u. Then mass of neutron by mass of an electron is 1.00867/0.00054 = 1838. THEREFORE the mass of neutron in terms of the electron is 1838 times.

Right CHOICE is (a) 400 – 750 nm

To elaborate: Electromagnetic spectrum is made up of various electromagnetic radiation. They are radio waves, X-RAYS, GAMMA rays, UV rays, the visible region, IR waves, and microwaves. Visible rays are the only ones which a HUMAN eye can see. They range from 450 – 750 nm.

The correct choice is (d) 2s

Best explanation: As per the Aufbau’s PRINCIPLE, the orbital or subshell with the lowest energy should be filled FIRST. The ascending order of orbital’s energy is given by 1s, 2s, 2p, 3S, 3p, 4s, 3d, 4p, 5S, 4d, 5p, 4f, 5d, 6P, 7s. So 2s orbital should be filled first.

The correct choice is (C) Threshold

Explanation: In the photoelectric effect, when PHOTONS strike on a metal surface, it emits electrons. Thus for emitting an electron, it requires a minimum AMOUNT of ENERGY. This is threshold energy acquired through threshold frequency.

Right choice is (B) 3 Hz

Explanation: The relation between wavelength(λ) and frequency(v) of a WAVE is given by λ = c/v where c is the SPEED of LIGHT of the light. v = c/λ Frequency of the given wave = (3 X 10^8m/s)/(10 x 10^-9m) = 3 Hz.

The correct CHOICE is (c) 32

For explanation: The number of orbitals within an ORBIT is n2. But as each orbital can ACCOMMODATE 2 electrons, the number of electrons that can exist with the “n” as the principal quantum number is 2n^2. So here 2n^2 = 2(4)^2 = 2(16) = 32.

Correct choice is (c) 19K^40

The BEST I can explain: Isobar is a species of an element having the same mass number but a DIFFERENT atomic number. As per the above QUESTION, only 19K^40 satisfies the conditions of 18Ar^40 to be its ISOTOPE.

Right answer is (a) R. A. Millikan

Best EXPLANATION: R. A. Millikan conducted oil drop experiment to measure the mass of oil droplets. After observation of how the charge is transferred in the experiment he CONCLUDED that charge only APPEARS in INTEGRAL multiples of e i.e. q = ne; n = ±1, ±2, ±3, etc.