What are the differences between jquery 1.x and jquery 2.x ?

Versions of2.x leave behind the older Internet Explorer6,7, and8 browsers. In return they are smaller, faster, and can be used in JavaScript environments where the code needed for old-IE compatibility often causes problems of its own. The jQuery team still supports the1.x branch which does run on IE6/7/8. You can (and should) continue to use jQuery1.9 (and the upcoming1.) on web sites that need to accommodate older browsers.

Basically in2.x they discontinue the support for IE6-8

Two versions of JQuery.

Versions of 2.x leave behind the older Internet Explorer 6, 7, and 8 browsers. 

In return they are smaller, faster

The jQuery team still supports the 1.x branch which does run on IE 6/7/8.

if you’re one of those lucky developers who has dropped support for IE6/7/8, grab jQuery 2.0 and don’t look back.