Assertion reason .....A: the particles of a suspension can be seen by naked eye R: when the suspension is left undisturbed it become unstable...,

Dear Student,

We can see clearly that both assertion and reason are true.
It's true that the particles of a suspension can be seen by the naked eye.
And The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable. 
Both the statements are true independently but Reason is not the Correct Explanation of Assertion.
Therefore the answer should be,
Both A and R are true and R is not the correct explanation of A.

Regards