You can't format free space because there's no partition on it.
I'm intrigued in your disk layout because I would have expected to see your C drive with Windows on it next to the 100MB system (boot) partition.
Did you once have more than one operating system or did you try to re-install Windows?
Whatever happened, you need to create a partion on the free space before you can format it.
I'd be inclined to delete the D partition then create a new partition on the resultant extended free space, which you can then format, although I am puzzled by the fact you've also got Windows on a logical partition, when ideally it should be on a primary partition.