How can I convert special characters to normal characters in an URL query string?
To generate URL we use url() function. l() function is used to generate a text with link. See the example below:

// Generate a Text with link
echo l('Link Text', 'node/' . $nid . '/delete', array('query' =&gt; array('destination' =&gt; 'chapter/' . $cnid)));

// Generate a Link.
echo url('node/' . $nid . '/delete', array('query' =&gt; array('destination' =&gt; 'chapter/' . $cnid)));