I Have studio 9 plus and in that i would select the clip and bring up the sound toolbox and just lower the volume on that one clip to nothing.

other than that the another way of doing it would be to copy that one chapter into a new project, delete the audio from it, render it out so you have a new version. then reopen the original project and replace the old chapter with the new silent one.

I hope I've understood you correctly and that this helps.