Let $\;z \neq -i\;$ be any complex number such that $\;\large\frac{z-i}{z+i}\;$ is a purely imaginary number . Then $\;z+ \large\frac{1}{z}\;$ is :

Question

(a) 0 \[\](b) any non - zero real number other than 1. \[\](c) any non-zero real number.\[\](d) a purely imaginary number