The radius of the second Bohr orbit, in terms of the Bohr radius, a...

Radius of Bohr's orbit is given as,

$r = \dfrac{{a}_{0}{n}^{2}}{Z}$

n = orbit number

Z = atomic number

For ${2}^{nd}$ Bohr's orbit of ${\text{Li}}^{\text{2+}}$

${Li}^{2 +}, r = \dfrac{{a}_{0}{\left(2\right)}^{2}}{3} = \dfrac{4{a}_{0}}{3}$