How to remove the .php extension from the URL ?

Ans : Add the following code in .htaccess file

======================
Options +FollowSymLinks
Options +Indexes
RewriteEngine on
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^([^\.]+)$ $1.php [NC,L]
======================

and same as for .html extension

======================
Options +FollowSymLinks
Options +Indexes
RewriteEngine on
RewriteCond %{SCRIPT_FILENAME} !-d
RewriteRule ^([^\.]+)$ $1.html [NC,L]
======================