Sub-atomic Particles — NEET Chemistry MCQs with Solutions
Free NEET 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. E. Rutherford
C. J. J. Thomson ✓ Correct
D. R. A. Millikan
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. Negatively charged particles (electrons) ✓ Correct
B. Electromagnetic waves
C. Positively charged particles
D. Neutral 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. $-1.6 \times 10^{-27}$ C
B. $-6.6 \times 10^{-34}$ C
C. $-9.1 \times 10^{-31}$ C
D. $-1.6 \times 10^{-19}$ C ✓ Correct
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. $1.6 \times 10^{-19}$ C/kg
B. $1.76 \times 10^{11}$ C/kg ✓ Correct
C. $6.02 \times 10^{23}$ C/kg
D. $9.58 \times 10^{7}$ C/kg
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 on the electron ✓ Correct
B. Charge-to-mass ratio of the electron
C. Mass of the proton
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. E. Goldstein
B. R. A. Millikan
C. J. J. Thomson ✓ Correct
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. Ernest Rutherford
B. James Chadwick ✓ Correct
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. J. J. Thomson
B. E. Goldstein ✓ Correct
C. R. A. Millikan
D. Niels Bohr
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. Depends on the gas taken in the tube
B. Is different for every discharge tube
C. Depends on the material of the cathode
D. Is independent of the nature of the gas in the tube ✓ Correct
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. Neon
B. Oxygen
C. Hydrogen ✓ Correct
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. $3.2 \times 10^{-30}$ kg
B. $1.6 \times 10^{-27}$ kg
C. $1.67 \times 10^{-27}$ kg
D. $9.1 \times 10^{-31}$ kg ✓ Correct
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. 3 ✓ Correct
B. 5
C. 2
D. 4
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. The atom is mostly empty space
B. Cathode rays are electromagnetic waves
C. The electron has no mass
D. Electric charge is quantized (an integral multiple of e) ✓ Correct
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. Zero
C. $+1.6 \times 10^{-19}$ C ✓ Correct
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 are deflected towards the negative plate in an electric field ✓ Correct
B. They can rotate a light paddle wheel placed in their path
C. They produce fluorescence on the glass wall
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. Proton
D. Positron
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. α-particle
B. Neutron
C. Proton
D. Electron ✓ Correct
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. Positive plate ✓ Correct
B. Neither plate
C. Both plates equally
D. Negative plate
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. 6 ✓ Correct
C. 3
D. 9
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. Neutron
B. Electron
C. Proton ✓ Correct
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. Carry no energy
B. Are positively charged
C. Possess mass (and hence momentum) ✓ Correct
D. Are electromagnetic waves
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. $1.76 \times 10^{11}$ C/kg
B. $9.58 \times 10^{7}$ C/kg ✓ Correct
C. $1.67 \times 10^{-27}$ 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. electron > proton > α-particle ✓ Correct
B. proton > electron > α-particle
C. α-particle > proton > electron
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. Cathode rays
B. Anode rays (canal rays) ✓ Correct
C. X-rays
D. γ-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. Much smaller than that of a proton
C. Exactly equal to that of an electron
D. Zero
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 rays travel faster
B. Cathode rays are positively charged
C. Positive ray particles are much heavier than electrons ✓ Correct
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. 4.5 electrons
D. 5 electrons ✓ Correct
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 was discovered before the electron
B. It carries a charge of −1.6 × 10⁻¹⁹ C
C. It is lighter than an electron
D. It is electrically neutral with mass close to that of a proton ✓ Correct
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. Charge-to-mass ratio (e/m) ✓ Correct
B. Velocity
C. Number
D. Colour
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.