/helper/dropdown_helper.php

<?php
	if(!defined('BASEPATH')) exit('No direct script access allowed');
 
 
	function listData($table, $name, $value, $orderBy='ASC'){
		$items = array();
		$CI =& get_instance();

		if($orderBy){
			$CI->db->order_by($value,$orderBy);
		}

		$query = $CI->db->select("$name,$value")->from($table)->get();

		if ($query->num_rows() > 0){
			foreach($query->result() as $data) {
		    	$items[$data->$name] = $data->$value;
		  	}

		  	$query->free_result();
		  	return $items;
		}
	}

/config/autoload.php

$this->load->helper('form',dropdown');

/controllers/test.php

<?php 

	class Test extends CI_Controller {
	    
	     public function index() {
	         $dropdownItems = listData('country_tbl','country_id', 'country_name');

	         echo form_dropdown('dropdown',$dropdownItems,$selected = 8);
	     }
	}