Sub-atomic Particles — JEE Main Chemistry MCQs with Solutions
Free JEE Main Chemistry Sub-atomic Particles MCQs with step-by-step solutions (30 questions). Part of Atomic Structure. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Sub-atomic Particles · easy · theory
The electron was discovered by:
A. James Chadwick
B. R. A. Millikan
C. E. Rutherford
D. J. J. Thomson ✓ Correct
Solution: J. J. Thomson (1897) studied cathode rays and established the existence of the electron, also measuring its charge-to-mass ratio.
Q2 — Sub-atomic Particles · easy · theory
Cathode rays are a stream of:
A. Electromagnetic waves
B. Neutral particles
C. Negatively charged particles (electrons) ✓ Correct
D. Positively charged particles
Solution: Cathode rays consist of electrons — negatively charged particles that travel from the cathode to the anode in a discharge tube.
Q3 — Sub-atomic Particles · easy · theory
The charge on a single electron is approximately:
A. $-9.1 \times 10^{-31}$ C
B. $-1.6 \times 10^{-19}$ C ✓ Correct
C. $-1.6 \times 10^{-27}$ C
D. $-6.6 \times 10^{-34}$ C
Solution: The magnitude of the electron's charge is 1.6 × 10⁻¹⁹ C, determined by Millikan. 9.1 × 10⁻³¹ kg is its mass, not charge.
Q4 — Sub-atomic Particles · easy · theory
The charge-to-mass ratio (e/mₑ) of the electron has a value of about:
A. $6.02 \times 10^{23}$ C/kg
B. $9.58 \times 10^{7}$ C/kg
C. $1.6 \times 10^{-19}$ C/kg
D. $1.76 \times 10^{11}$ C/kg ✓ Correct
Solution: Thomson measured e/mₑ = 1.76 × 10¹¹ C/kg for the electron. (9.58 × 10⁷ C/kg is the value for the proton.)
Q5 — Sub-atomic Particles · easy · theory
Millikan's oil drop experiment was designed to determine the:
A. Charge-to-mass ratio of the electron
B. Mass of the proton
C. Charge on the electron ✓ Correct
D. Radius of the nucleus
Solution: Millikan's oil drop experiment measured the charge on the electron (1.6 × 10⁻¹⁹ C) and showed that charge is always an integral multiple of this value.
Q6 — Sub-atomic Particles · easy · theory
The charge-to-mass ratio (e/m) of the electron was first determined by:
A. J. J. Thomson ✓ Correct
B. R. A. Millikan
C. E. Goldstein
D. J. Chadwick
Solution: Thomson determined e/m of the electron by studying the deflection of cathode rays in electric and magnetic fields.
Q7 — Sub-atomic Particles · easy · theory
The neutron was discovered by:
A. James Chadwick ✓ Correct
B. Ernest Rutherford
C. J. J. Thomson
D. E. Goldstein
Solution: James Chadwick (1932) discovered the neutron by bombarding beryllium with α-particles, producing a neutral radiation.
Q8 — Sub-atomic Particles · easy · theory
Anode rays (canal rays), which led to the discovery of the proton, were first observed by:
A. E. Goldstein ✓ Correct
B. Niels Bohr
C. R. A. Millikan
D. J. J. Thomson
Solution: E. Goldstein (1886) discovered canal rays (anode rays) using a perforated cathode; the lightest positive particle (from hydrogen) was later identified as the proton.
Q9 — Sub-atomic Particles · medium · theory
The value of e/m for a cathode ray particle:
A. Is different for every discharge tube
B. Is independent of the nature of the gas in the tube ✓ Correct
C. Depends on the material of the cathode
D. Depends on the gas taken in the tube
Solution: The e/m of cathode rays is the same regardless of the gas or electrode material, proving that electrons are a universal constituent of all atoms.
Q10 — Sub-atomic Particles · medium · theory
For anode (positive) rays, the charge-to-mass ratio (e/m) is maximum when the gas taken in the discharge tube is:
A. Hydrogen ✓ Correct
B. Oxygen
C. Neon
D. Nitrogen
Solution: e/m of positive rays depends on the gas and is largest for hydrogen, because the H⁺ ion (proton) has the smallest mass.
Q11 — Sub-atomic Particles · medium · numerical
Using e = 1.6 × 10⁻¹⁹ C and e/mₑ = 1.76 × 10¹¹ C/kg, the mass of the electron is approximately:
A. $1.67 \times 10^{-27}$ kg
B. $1.6 \times 10^{-27}$ kg
C. $9.1 \times 10^{-31}$ kg ✓ Correct
D. $3.2 \times 10^{-30}$ kg
Solution: mₑ = e ÷ (e/mₑ) = (1.6 × 10⁻¹⁹) ÷ (1.76 × 10¹¹) ≈ 9.1 × 10⁻³¹ kg.
Q12 — Sub-atomic Particles · medium · numerical
In a Millikan-type experiment, an oil drop carries a charge of 4.8 × 10⁻¹⁹ C. The number of excess electrons on the drop is:
A. 4
B. 2
C. 3 ✓ Correct
D. 5
Solution: Number of electrons = total charge ÷ electron charge = (4.8 × 10⁻¹⁹) ÷ (1.6 × 10⁻¹⁹) = 3.
Q13 — Sub-atomic Particles · medium · theory
The most important conclusion drawn from Millikan's oil drop experiment is that:
A. Electric charge is quantized (an integral multiple of e) ✓ Correct
B. Cathode rays are electromagnetic waves
C. The electron has no mass
D. The atom is mostly empty space
Solution: Every measured drop carried a charge that was a whole-number multiple of 1.6 × 10⁻¹⁹ C, showing charge is quantized.
Q14 — Sub-atomic Particles · easy · theory
The charge present on a proton is:
A. $+3.2 \times 10^{-19}$ C
B. $+1.6 \times 10^{-19}$ C ✓ Correct
C. Zero
D. $-1.6 \times 10^{-19}$ C
Solution: The proton carries a positive charge equal in magnitude to the electron's charge: +1.6 × 10⁻¹⁹ C.
Q15 — Sub-atomic Particles · medium · numerical
A proton is heavier than an electron by a factor of approximately:
A. 1836 ✓ Correct
B. 9100
C. 1000
D. 100
Solution: mₚ/mₑ ≈ (1.67 × 10⁻²⁷)/(9.1 × 10⁻³¹) ≈ 1836.
Q16 — Sub-atomic Particles · medium · theory
Which of the following is NOT a property of cathode rays?
A. They produce fluorescence on the glass wall
B. They are deflected towards the negative plate in an electric field ✓ Correct
C. They can rotate a light paddle wheel placed in their path
D. They travel in straight lines
Solution: Cathode rays are negatively charged, so they are deflected towards the POSITIVE plate, not the negative plate. The other statements are all true.
Q17 — Sub-atomic Particles · medium · theory
The neutron was produced by bombarding a beryllium target with α-particles: ⁹Be + ⁴He → ¹²C + X. The particle X is a:
A. Neutron ✓ Correct
B. Electron
C. Positron
D. Proton
Solution: Balancing mass number (9 + 4 = 13 = 12 + 1) and charge (4 + 2 = 6 = 6 + 0), X has mass number 1 and charge 0 — a neutron.
Q18 — Sub-atomic Particles · medium · theory
Which of the following particles has the largest charge-to-mass ratio?
A. Electron ✓ Correct
B. Proton
C. Neutron
D. α-particle
Solution: The electron has by far the smallest mass with a full unit of charge, giving it the largest e/m ratio. (A neutron has zero charge, so its ratio is zero.)
Q19 — Sub-atomic Particles · easy · theory
In an electric field, cathode rays are deflected towards the:
A. Negative plate
B. Neither plate
C. Both plates equally
D. Positive plate ✓ Correct
Solution: Being negatively charged, cathode ray electrons are attracted to and deflected towards the positive plate.
Q20 — Sub-atomic Particles · medium · numerical
How many electrons are required to make up a total charge of −9.6 × 10⁻¹⁹ C?
A. 12
B. 3
C. 9
D. 6 ✓ Correct
Solution: Number of electrons = (9.6 × 10⁻¹⁹) ÷ (1.6 × 10⁻¹⁹) = 6.
Q21 — Sub-atomic Particles · easy · theory
The particle that has a mass of about 1 atomic mass unit and a charge of +1 is the:
A. Electron
B. Proton ✓ Correct
C. Neutron
D. Positron
Solution: The proton has mass ≈ 1 u and charge +1. The neutron also has mass ≈ 1 u but is neutral; the electron is far lighter.
Q22 — Sub-atomic Particles · medium · theory
The fact that cathode rays can rotate a small paddle wheel placed in their path shows that they:
A. Are electromagnetic waves
B. Possess mass (and hence momentum) ✓ Correct
C. Carry no energy
D. Are positively charged
Solution: The mechanical (rotational) effect on a paddle wheel demonstrates that cathode ray particles have mass and momentum.
Q23 — Sub-atomic Particles · medium · theory
The charge-to-mass ratio (e/m) of the proton is approximately:
A. $1.67 \times 10^{-27}$ C/kg
B. $9.58 \times 10^{7}$ C/kg ✓ Correct
C. $1.76 \times 10^{11}$ C/kg
D. $1.6 \times 10^{-19}$ C/kg
Solution: e/mₚ = (1.6 × 10⁻¹⁹)/(1.67 × 10⁻²⁷) ≈ 9.58 × 10⁷ C/kg — about 1836 times smaller than the electron's value.
Q24 — Sub-atomic Particles · medium · theory
The correct order of the specific charge (e/m) of the electron, proton and α-particle is:
A. proton > electron > α-particle
B. α-particle > proton > electron
C. electron > proton > α-particle ✓ Correct
D. electron > α-particle > proton
Solution: The electron's tiny mass gives the highest e/m. Proton (charge +1, mass 1u) exceeds the α-particle (charge +2, mass 4u ⇒ ratio ∝ 2/4 = 0.5 per unit).
Q25 — Sub-atomic Particles · easy · theory
The discovery of the proton is associated with the study of:
A. γ-rays
B. Anode rays (canal rays) ✓ Correct
C. X-rays
D. Cathode rays
Solution: Positive (anode/canal) rays, produced from a perforated cathode, led to the identification of the proton as the lightest positive particle (from hydrogen).
Q26 — Sub-atomic Particles · medium · theory
The mass of a neutron is:
A. Slightly greater than that of a proton ✓ Correct
B. Zero
C. Much smaller than that of a proton
D. Exactly equal to that of an electron
Solution: The neutron (1.675 × 10⁻²⁷ kg) is very slightly heavier than the proton (1.672 × 10⁻²⁷ kg) and is electrically neutral.
Q27 — Sub-atomic Particles · medium · theory
The e/m ratio of positive rays is smaller than that of cathode rays mainly because:
A. Positive ray particles are much heavier than electrons ✓ Correct
B. Cathode rays are positively charged
C. Positive rays travel faster
D. Positive rays carry no charge
Solution: Positive ray particles are ionised atoms/molecules — thousands of times heavier than electrons — so for a comparable charge their e/m is far smaller.
Q28 — Sub-atomic Particles · medium · theory
An oil drop is found to carry a charge of 8.0 × 10⁻¹⁹ C. This observation is consistent with the drop having:
A. 2 electrons
B. 8 electrons
C. 5 electrons ✓ Correct
D. 4.5 electrons
Solution: (8.0 × 10⁻¹⁹)/(1.6 × 10⁻¹⁹) = 5. Charge must be a whole-number multiple of e, so 5 electrons — never a fractional number.
Q29 — Sub-atomic Particles · easy · theory
Which statement about the neutron is correct?
A. It is electrically neutral with mass close to that of a proton ✓ Correct
B. It was discovered before the electron
C. It carries a charge of −1.6 × 10⁻¹⁹ C
D. It is lighter than an electron
Solution: The neutron is neutral, has a mass just above the proton's, and was discovered (1932) long after the electron (1897).
Q30 — Sub-atomic Particles · medium · theory
The property of cathode rays that is independent of the material of the electrodes and the nature of the gas is their:
A. Colour
B. Velocity
C. Number
D. Charge-to-mass ratio (e/m) ✓ Correct
Solution: The constant e/m of cathode rays, whatever the gas or electrode, was the key evidence that electrons are fundamental constituents of all matter.