Step 1: Know the two terms:
A formal organisation is planned by management. An informal organisation grows from social ties. We compare them on authority, leadership and flow of communication.
Step 2: (i) Authority:
Formal organisation: authority arises by virtue of a position in the management. A manager has power because of his post.
Informal organisation: authority arises out of personal qualities. A person with knowledge or a pleasant nature gets influence.
Step 3: (ii) Leadership:
Formal organisation: the managers are the leaders.
Informal organisation: the leaders may or may not be managers. The group chooses them.
Step 4: (iii) Flow of communication:
Formal organisation: communication takes place through the scalar chain, from one level to the next.
Informal organisation: the flow of communication does not follow a planned route. It can move in any direction.
Final Answer:
Formal organisation has position based authority, manager leaders and scalar chain communication. Informal organisation has authority from personal qualities, group chosen leaders and free communication.