Question how to find positive and negative pins on arduino

[Siddharth Thakur.]

How do i distinguish Pins on arduino are positive and negative ? at pin 13 there is an inbuild led, but how only 1 pin connet to an led? an led need both positive and negative terminals, so please help me with this.

 

[Lutfij]

Considering you have P13 as +ve, you can treat the other end by connecting to a ground.