Cause : (noun)
( 1) That which produces an effect, thing, event, person, etc…make something happen
What was the cause of the fire?
Smoking is one of the causes of heart disease.
( 2) Aim, principle or movement that is strongly defended or supported
His life was devoted to the cause of justice.
Cause : (verb)
( 1) Make happen
Be a cause of something
Smoking can cause lung cancer.
She is always causing trouble for people.
The cold weather caused the plants to die.
Reason : (noun)
( 1) Motive or justification for something
Give me the reason for your going.
He has adequate reason for doing so.
( 2) Power of the mind to think, understand, form opinion, etc…
Only man has reason.
( 3) What is right or practical or possible
There is a good deal of reason in what you say.
( 4) CAUSE of something is what makes something happen.
The police are investigating the cause of the explosion.
( 5) REASON for something has a wider use. It can be the explanation that people give for why something is done.
( 6) What was the reason for his resignation?
She did not give any reason for leaving.