Let $X$ be a Banach space, and $I$ be a closed subspace. Then it's known that $(X/I)^*=I^{\perp}$. My question is what is the second dual of $X/I$? or what is the dual of $I^{\perp}$ ?
If we know that $(X/I)$ is reflexive, does this give any additional information about $I$, and about $(I^{\perp})^*$ rather than being reflexive of course!
Thank you in advance.