Problems with Arduino on Mac

Using Arduino Installation & Troubleshooting
#1

hey, i can't communicate with my arduino on my mac.

i have Yosemite, newest software version of arduino and arduino uno R3.There is no choosing option for arduino uno in the board menu

https://app.box.com/s/eves7qe8b7tdnvi2t3upi9jpczpakhej

can you help me?

#2

You already have it chosen: "Arduino/Genuino Uno".

#3

i got sync errors between the mac and arduino

#4

Sync errors means that the responses from the bootloader are not as expected. What, exactly, do the RX and TX LEDs on the Arduino do when you try an upload?

#5