Let's see
According to bohrs model
[tex]\\ \rm\Rrightarrow r\propto n^2/Z^2[/tex]
[tex]\\ \rm\Rrightarrow r= r_on^2/Z^2[/tex]
[tex]\\ \rm\Rrightarrow r=0.529\times \dfrac{5^2}{1^2}[/tex]
[tex]\\ \rm\Rrightarrow r=0.529(25)[/tex]
[tex]\\ \rm\Rrightarrow r=1.32nm[/tex]
