Match List I with List II
| LIST I | LIST II | ||
|---|---|---|---|
| A. | Mass of alpha particle | I. | 1.00727 u |
| B. | Mass of proton | II. | 4.00260 u |
| C. | Mass of neutron | III. | 0.00055 u |
| D. | Mass of electron | IV. | 1.00866 u |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-II, B-I, C-IV, D-III
Masses on the atomic scale are measured in the atomic mass unit u, one-twelfth of the mass of a carbon-12 atom. A nucleon has a mass close to 1 u, and the neutron is slightly heavier than the proton.
(A) Mass of alpha particle — this matches (II) 4.00260 u. An alpha particle is a helium-4 nucleus of two protons and two neutrons, so its mass is close to 4 u; this is the only value near 4 u.
(B) Mass of proton — this matches (I) 1.00727 u. Of the two values close to 1 u, the proton has the smaller one.
(C) Mass of neutron — this matches (IV) 1.00866 u. The neutron is the heavier nucleon, by about 0.0014 u.
(D) Mass of electron — this matches (III) 0.00055 u. The electron is about 1840 times lighter than a proton, so its mass is a tiny fraction of 1 u.
NCERT (2026-27):
Atomic Masses and Composition of Nucleus – “… The mass of a proton is
\( \displaystyle m_p = 1.00727\,\mathrm{u} = 1.67262\times10^{-27}\,\mathrm{kg} \qquad (13.2) \)
This is equal to the mass of the hydrogen atom (= 1.00783u), minus the mass of a single electron (me = 0.00055 u). … The mass of a neutron is now known to a high degree of accuracy. It is
\( \displaystyle m_n = 1.00866\,\mathrm{u} = 1.6749\times10^{-27}\,\mathrm{kg} \qquad (13.3) \)”