Question

format of formal and informal letter as per icse board exam

Answer 1

(arrows mean  you have to leave a line,)
Formal

Sender's address
(make it in four/ three lines, both the addresses. e.g
e-401,
A.B.C Apartments,
X.Y.Z city
Pin-code)
P.S: if writing from a company/group, write the office address
→
Date 
→
To, (the designation of the person whom you are writing the letter)
Receiver's address 
→
Subject: (it is generally given in the question and make it brief)
→
Dear Sir/Mam,
(your intro eg. I am XYZ from so and so ) and i may like throw ight on the topic/ make a complain/ (anything else as per the the question)
THE BODY IS OF 3 PARAGRAPHS (max)
(Last line) i.e I am sure you will take a look at the matter. 
→
Thanking you,
Your name,
Designation (if from a commitee)
Address
⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻

INFORMAL

Sender's address (four/three lines)
→
Date
→
Dear XYZ,
May this letter find you in pink of health.
(min. 2 para. max. 3 para)
(Last line) Convey my warm regards to Uncle/Aunty/Mom/Dad/Grandpa/Grandma
→
Yours Lovingly/Truly (or you can use Truly Yours)
Your name

Note: Make the informal letter little personal. Add your feelings.

Answer 2

address
date
dear
start
conclusion
thankyou
your sincerely