The radius of the first orbit in Bohr's hydrogen atom is 0.53 Å. The radius of fourth orbit of this atom will be:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 8.48 Å
In Bohr’s model of the hydrogen atom the radius of the nth orbit is proportional to \( n^{2} \): \( r_n = n^{2}r_1 \).
\( r_4 = 4^{2}\times0.53\,\mathrm{\mathring{A}} = 16\times0.53\,\mathrm{\mathring{A}} \)
\( r_4 = 8.48\,\mathrm{\mathring{A}} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
