With one look how to know if The RAM is DDR 1 , 2 or 3 and its DATA Rate and i really mean just one look ?i

It depends on the exprience but you can tell by looking the chips on the RAM stick, Pins and cut location.

DDR1has thick chips whereas DDR2 and3 have skinny chip patterns.

Nobody have time to count the pins so the best way is to check the cut  location and chip pattern.

The RAM stick will always have a sticker and/or imprinted information which shows what type of RAM it is, look for it.