Q: Can I use one single 8GB memory stick in 2012 mac mini ?

http://www.crucial.com/uk/index.aspx?cm_mmc=onsite-_-refer-_-cntrycode-_-GB

Quote from Apples Knowledge Base:

"Your Mac mini came with at least 2 gigabytes (GB) of memory on a pair of 1 GB

memory modules. You can replace these with a pair of 2 GB or 4 GB memory modules,

for a maximum of 8 GB of memory."

Use Crucials adviser to spec and cost the correct RAM for your Mini:

Crucial

Yes, the 2102 mini can take a maximum of 16 GB in two 8 GB sticks. With only one stcik, memory waccess will be slow since dual channel mode can;t be used.

I have no idea when Gary Scotland says

"Your Mac mini came with at least 2 gigabytes (GB) of memory on a pair of 1 GB

memory modules. You can replace these with a pair of 2 GB or 4 GB memory modules,

for a maximum of 8 GB of memory."

since here:

http://support.apple.com/kb/HT4432#1

Apple says

• 16 GB for Mac mini (Late 2012)

and here
http://support.apple.com/kb/HT5475

appl says

You can use RAM module sizes of 2 GB, 4 GB or 8 GB in each slot. For best performance, don't mix sizes of memory modules.