The ratio of the radius of the third orbit to that of the second orbit in a hydrogen atom is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 9:4 \)
In the Bohr model the radius of the \( n \)th orbit of hydrogen is proportional to \( n^{2} \).
\( \displaystyle r_n = n^{2}\,a_0 \;\Rightarrow\; \frac{r_3}{r_2} = \frac{3^{2}}{2^{2}} = \frac{9}{4} \)
So the ratio is \( 9:4 \).