# Given that, $r_{(n+1)}-r_n=r_{(n-1)}$,where $r_n,r_{n-1}$ and $r_{(n+1)}$ are Bohr's radius for H-atom in $n^{th},(n-1)^{th}$ and $(n+1)^{th}$ shell respectively.
$(a)\;3\qquad(b)\;2\qquad(c)\;4\qquad(d)\;5$