while filling up form I 821 i need inforamtion for part 2 what do I write in no 4 alien registrtaion no? 

If you have any EAD cards from before there is a alien number on it. Write that number. No 5 uscis Elis account no?

Not needed. 6 us socila security no? I dont have social security no - Leave blank

25 (b)date authorized period of stay ? because my visa is expired already but i have I20 with validity It should be on your I-94 card. If you came on F1 then you need to write D/S. Since it just take date on it. You need to first fill all other info, save it in PDF file, print it then write D/S(if came to US on F1 visa). Don't know about other. Hope it helps.