(d)
According to Bohr model,
Radius of hydrogen atom
$\left( r_{n} \right) = \frac{0.529 \times n^{2}}{Z}\mathring{\mathrm{A}}$
(where, $n$=number of orbit, $Z$=atomic number)
$r_{3} = \frac{0.529 \times (3)^{2}}{1} = 4.761\mathring{\mathrm{A}}$