Match Column A with Column B.
| Column A | Column B |
| 1. Mass of the electron | A. \( \sim10^{-10}\,\mathrm{m} \) |
| 2. Size of an atom | B. \( 1.673\times10^{-27}\,\mathrm{kg} \) |
| 3. Mass of the proton | C. \( 9.1\times10^{-31}\,\mathrm{kg} \) |
| 4. Size of the nucleus | D. \( \sim10^{-15}\,\mathrm{m} \) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 1-C, 2-A, 3-B, 4-D
The electron is the lightest particle in the atom. The nucleus is about 10,000 to 100,000 times smaller than the atom.
1. Mass of the electron — This matches C, \( 9.1\times10^{-31}\,\mathrm{kg} \). The electron is far lighter than the proton, about 1840 times lighter.
2. Size of an atom — This matches A, \( \sim10^{-10}\,\mathrm{m} \). The size of an atom was known from kinetic theory to be about \( 10^{-10}\,\mathrm{m} \).
3. Mass of the proton — This matches B, \( 1.673\times10^{-27}\,\mathrm{kg} \). The proton, the nucleus of the lightest hydrogen atom, has a mass of 1.00727 u, about \( 1.673\times10^{-27}\,\mathrm{kg} \).
4. Size of the nucleus — This matches D, \( \sim10^{-15}\,\mathrm{m} \). Rutherford’s experiments gave the size of the nucleus as about \( 10^{-15} \) m to \( 10^{-14} \) m.
NCERT (2026-27):
Example 11.3 – “… (a) For the electron: Mass m = 9.11×10–31 kg, speed v = 5.4×106 m/s.”
Alpha-particle Scattering and Rutherford’s Nuclear Model of Atom – “… Rutherford’s experiments suggested the size of the nucleus to be about 10–15 m to 10–14 m. From kinetic theory, the size of an atom was known to be 10–10 m, about 10,000 to 100,000 times larger than the size of the nucleus.”
Atomic Masses and Composition of Nucleus – “… The nucleus of the lightest atom of hydrogen, which has a relative abundance of 99.985%, is called the proton. The mass of a proton is”
\( m_p=1.00727\,\mathrm{u}=1.67262\times10^{-27}\,\mathrm{kg} \)\( \qquad (13.2) \)