A function f is defined on interval (0, 1) as follows f(x)-1 when x is rational no. and icm(p.g)=1 when x is irational fis continuous at each irrational point a

A function f is defined on interval (0, 1) as follows f(x)-1 when x is rational no. and Icm(p.g)=1 when x is irational fis continuous at each irrational point and discontinuous at each rational point fis continuous at each rational point and discontinuous at each irational point fis discontinuous at each rational and irrational points fis continuous at each rational and irrational points please explain the answer