In Bohr's atomic model, the radius of the first orbit is \( r_o \). The radius of the third orbit will be:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 9r_o \)
In Bohr's model the radius of the \( n \)th orbit grows as the square of the quantum number:
\( \displaystyle r_n = r_o\,n^{2} \)
\( \displaystyle r_3 = r_o \times 3^{2} = 9r_o \)