Assertion(A) : The  highest oxidation state osmium ‘+8’ 
Reason (R):    Osmium is a  $5d-block$  element
 

Both (A) and (R)  are true  but (R) is not correct explanation of(A)

Both (A)  and (R) are true and the (R) is the correct explanation of the (A)

(A)  is not ture but (R) is true

Both (A) and (R) are false