Question mark on an atom?

I could not interpret the question mark(?) on an atom. Could anyone tell me how to fix this issue?

A screenshot is attached.

Thanks.

Noel

Hi,

The question mark notes that the stereochemistry of the atom is unkown, but it is a possible stereo center.

These are shown when the View>Stereo>R/S Labels>All possible option is selected, you can find information about the available options and how they work in the documentation here.

Regards,
Istvan