Will this work on my IIc?

First off, I think that the description is incorrect and that this is a 400k disk drive, not 800k. (Which means that it won't work no matter what.) If you're going to get an Apple brand 800k drive (say from Ebay) make sure that it's the kind with the slots on the top of the case (the smooth topped ones are the 400k variety).

Secondly it depends on what type of Apple //c you have. The first ones issued (model #4000) had a timing problem (with the modem) and could only handle one external 5.25" floppy. They did have a free motherboard exchange program that some people could/did take advantage of if they found out about it. This fixed the modem problem and also upgraded the hardware so that a user could use an either an external 5.25"(140k) or 3.5"(800k drive). The second release of the //c, (model #4100) had these features standard.

An Apple //c plus can have up to five external disk drives hooked up (daisychained), two 5.25" and three 3.5", or fewer in combination.

To answer your second querry, most external apple brand 5.25" drives will work, but not the very common Disk ][ (at least not without a cable adapter). Even a dual drive will work, but you'll only be able to access one of the drives.

I've had a bunch of these over the years (with Macs 128K, 512K and Plus) and I'm 99.8% sure it's an 800K drive.

As for the rest I have zero idea as I've never used an Apple II.

dan k

That's a Mac 800k drive. It won't work with any IIc. There is only one 3.5" drive that'll work with some IIc and that's the 3.5" UniDisk. Most early IIc won't work with the 3.5" UniDisk without a ROM upgrade. To see if your IIc will work with the 3.5" UniDisk in basic enter PRINT PEEK(64447) and press return. If the number on screen is 255 you can't use the 3.5" UniDisk. If it's any other number you can.
Any Apple 5.25" drive with a 19 pin connector will work with a IIc

Wayne