Gogeto_16 :
ok bro I understand this was very helpful for me but last thing you are saying that i5-6500 will bottle neck???? so I should buy 7400 or 6500 and i'm okay with 1 slot mobo but tell me a mobo with 4 slots of RAM and 1 slot of GPU and I can only buy rx 460 will it be enough this was the last question please after i'm done with it
The problem with DX11 games is that the GPU's driver has much more work to do (compared with DX12 or Vulkan), and most of that work is done on a single thread - so it's very dependent on the CPU's single core performance. As this specific i5 is clocked quite low, your system may actually be CPU bottlenecked. Now, it may mean that a specific game cannot go past 45 fps at max settings while the GPU is idling and 3/4th of your CPU cores underused, or you may just not notice it because your GPU can't handle more than that anyway. It's a bottleneck, but not a HUGE one.
The RX460 is a very low performing card; it's geared towards e-sports (strategy, etc.) and occasional gaming; there's NO WAY you'd be CPU-bottlenecked with it. The 1050Ti is currently at the sweet spot for entry level gaming, so go for it. If you want to stay on budget, either get the Pentium to prevent driver bottlenecking on DX11 games at the cost of less raw horsepower on other apps but more budget for the rest of the system (to get a 256 Gb SSD, for example, or a RX470, which does kick ass on newer games), or go with the i5 for better smoothness at the cost of no crazy high fps.
AS for the mobo, the MSI B150M Pro-VDH will cost ten bucks more but comes with 4 DDR4 slots.