ans should be B
event X =HH _
event Y= _ _T so X and Y are independent so option A is out
event Z = 2T 1 H (any order TTH,THT,HTT) so if X occurs Z can not occur hence X and Z are dependent events so option D is out
event Z = 2T 1 H ( TTH(event Y is not possible hence Y and Z are dependent) ,THT(event Y is possible) ,HTT (event Y is possible)
consider choice C and D the question is asked about 2 (exactly 2) tails occur in 3 tosses now if there is a tail in 3rd toss then we need only one tail in first 2 tosses else we need 2 tails hence they are dependent on each other