Match List I with List II
| LIST I | LIST II |
| A. Size of nucleus | I. A - Z |
| B. Number of protons in \( {}^{A}_{Z}\mathrm{X} \) | II. Z |
| C. Size of atom | III. \( 10^{-10}\,\mathrm{m} \) |
| D. Number of neutrons in \( {}^{A}_{Z}\mathrm{X} \) | IV. \( 10^{-15}\,\mathrm{m} \) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-IV, B-II, C-III, D-I
In the symbol \( {}^{A}_{Z}\mathrm{X} \), \( Z \) is the atomic number (number of protons) and \( A \) is the mass number (protons plus neutrons). The nucleus is about \( 10^{5} \) times smaller than the atom.
(A) Size of nucleus — this matches (IV) \( 10^{-15}\,\mathrm{m} \). The nuclear radius is \( R = R_0 A^{1/3} \) with \( R_0 \approx 1.2\times10^{-15}\,\mathrm{m} \), a few femtometres.
(B) Number of protons in \( {}^{A}_{Z}\mathrm{X} \) — this matches (II) Z. The atomic number counts the protons.
(C) Size of atom — this matches (III) \( 10^{-10}\,\mathrm{m} \). Atoms are about an angstrom across; the Bohr radius of hydrogen is \( 0.53\times10^{-10}\,\mathrm{m} \).
(D) Number of neutrons in \( {}^{A}_{Z}\mathrm{X} \) — this matches (I) A - Z. The mass number counts protons and neutrons together, so the neutrons are \( N = A - Z \).
NCERT (2026-27):
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.”
Atomic Masses and Composition of Nucleus – “… The composition of a nucleus can now be described using the following terms and symbols:
Z – atomic number = number of protons [13.4(a)]
N – neutron number = number of neutrons [13.4(b)]
A – mass number = Z + N = total number of protons and neutrons [13.4(c)]”