Considering you have a 50/50 chance on each flip, you'd have so many combinations of what it could do.
H = Heads
T = Tails
HHHH = 4 heads
HHHT = 3 heads | 1 tail or 3 tails | 1 head
HHTT = 2 heads | 2 tails
TTTT = 4 tails.
Considering the immense amount of combinations, the answer would be:
1/16 chance because you have 4 different combinations of possibilities in the coinflip.
