75 as well as 100MM. But this one appears to be not a VESA standard.
http://www.samsung.com/us/system/consumer/product/ls/24/f9/ls24f9nsmza/FX2490HD_DSHT.pdf
"Optional wall mount kit available for purchase"
I'd try Samsungparts.com next.
Bob
I am trying to find a full motion desktop mount for my 24 inch Samsung FX2490HD monitor. There are four holes in the back for mounting, but so far Samsung has been no help in either selling or suggesting anything to me.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic