Ruby Scope

Dear Priyank,
Your question is not a surprise since WordPress is more popular than ROR and PHP. WordPress is a content management system developed with PHP. WordPress has a market share of 90.5% (as of Jan 2017). WordPress is used by 58.6% of all the websites whose content management system we know. This is 27.4% of all websites. (according to W3Tech). PHP is a programming language (PHP: Hypertext Preprocessor), which is used to build WordPress CMS. To Answer your question:
If you like to have a Content Management System for your website - WordPress is a good choice. If you want to write your own Content Management System or anything sort of a complex custom web application, you would really require PHP. If you like to extend WordPress with your own custom plugins - you will still require PHP, HTML and CSS.