White chalk?
I can only think of two things that are white and common
1- hard water stain.
Often times, water left to dry on leaves with turn into a white stain of the leave. It easily comes off with a wipe of wet towel.
2- Mealy bug
these guys are often seem as white fluffy things that will harm your orchid. It should be treated for.
As for the leaf, Where is it? I wouldn't pull any leavs if they were still alive. But if its the bottom, maybe pull it or cut it so no infection from the scar.
but please add photo so we can be more certiain help you
If you can post picture, try this
How To Upload Pictures and Post Them