Which parameter do I need to pass for user registration?
$user_data["field_name_first"]["en"][0]["value"]='testranjeet8';
$user_data["field_name_last"]["und"][0]["value"]='testgholave8';
$user_data["mail"]="testranjeet12@example.com";
$user_data["pass"]["pass1"]="test123458";
$user_data["pass"]["pass2"]="test123458";
$user_data["field_gender"]["en"]="Male";


Just pass the parameter you will get the result .I had problem with android side that they are not passing value correctly 
finally i got answer