The radius of the innermost electron orbit of a hydrogen atom is \( 5.3\times10^{-11}\,\mathrm{m} \). The radius of the third orbit is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( 4.77\times10^{-10}\,\mathrm{m} \)
In Bohr's model the radius of the nth orbit of hydrogen is proportional to \( n^{2} \), \( r_n = n^{2}r_1 \), where \( r_1 \) is the radius of the innermost (first) orbit.
\( r_3 = 3^{2}\times5.3\times10^{-11}\,\mathrm{m} = 47.7\times10^{-11}\,\mathrm{m} = 4.77\times10^{-10}\,\mathrm{m} \)
Note: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.
NCERT (2026-27):
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