Change your code to below.
<?php
mysql_connect("localhost","root","password");
mysql_select_db("rohan_iksha");
$towerValue_4bhk = $_GET['towerValue_4bhk'];
$floor_names_query = MYSQL_QUERY("select ".$total_4bhk." from project_master");
mysql_close();
?>
Run below code to check if your query is returning result.
<?php
$link = mysql_connect("localhost", "root", "password");
mysql_select_db("rohan_iksha", $link);
$result = mysql_query("select total_4bhk from project_master", $link);
$num_rows = mysql_num_rows($result);
echo "$num_rows Rows\n";
?>
See what it is returning.