out of these 2 cpus what is better for gaming and muit tasking like facebook youtube etc. intel G2100 or amd Phenom ii x4 965 BE
They'll both do Intenet stuff just fine, even a crappy Atom or E-XX APU will do that. What will be the deciding factor will be what games you are playing.
generally, intel seems to enjoy the benefit of single to dual core optimized games due to having a better ipc with their newer architecture. with the phenom being a quad core, it makes use of multi threaded optimization and the fact that it can overclock is nice as well(and AM3+ isnt dead yet when it comes to upgrade options in the future). For current games, Intel has an advantage in general, but more and more games will start to optimize more cores soon. The PS4 is already confirmed for 8 cores, and Microsofts infinity will probably have more than 3 cores as well if i had to guess. The trend is shown through optimizations in crysis, as Crysis uses the FX-8350(8 module cpu) so well, it actually beat the 2500k in performance.