What is the default Joomla 2.5 article url?

The default url for Joomla 2.5 to access a specific article without creating a menu link is:

index.php?option=com_content&view=article&id=22

The number at the end, in this case 22, is the id of your article. You can find this number in your article manager on the right hand side. 

Just add that string after yourwebsitename.com, correct the article id at the end to your article. 

For example:
http://www.yourwebsitename.com/index.php?option=com_content&view=article&id=22