What is difference between selenium 2 and selenium 3?

Selenium 2

Selenium2 is nothing but integration of WebDriver with Selenium RC(Selenium1). Selenium 1 is a well-established framework that supports various many browsers due to its JavaScript implementation. To step out of JavaScript Sandbox, WebDriver is developed for each browser which provides a headless browser emulator which is very speedy. The strengths of both WebDriver and Selenium 1 are imbibed in Selenium2 which also helps in getting rid of their respective drawbacks.

Selenium 3

For users of WebDriver API’s, this is a drop-in replacement. The major change being, removing the core and replacing it with the back-end WebDriver. Selenium 3.0 has become a W3C (world wide web consortium) standard. Also, Selenium 3 would be majorly looking to be a choice of software testing tool for both web and mobile-based applications.

Let's understand to compile the entire list of features which separate the two −

Selenium 2Selenium 3
Selenium 2 is the combination of WebdDriver+SeleniumRC (Selenium1) which is based on selenium core.The core is removed from Selenium3 but supports Selenium RC indirectly through back-end Webdriver.
WebDriver contributes its object-oriented API for Document Object Model (DOM) interaction and browser control. Firefox is the default browser.Browser vendors will ship their own WebDriver implementation, hence are tightly coupled to the browser giving a better testing experience.
Supports both the Selenium RC API, and the Selenium RC technology underneath the WebDriver API.No Web Driver API. GeckoDriver has been introduced for Firefox (v47 and above) regardless of any version of Selenium.
Mozilla, Chrome, IE implant their driver which is developed by Selenium developers.Modern Browsers such as Edge, Safari are introduced with the WebDrivers shipped by their vendors
Use of AndroidDriver and iPhone driver for mobile Automation.Use tools such as Appium for Mobile Automation.