Since either coin can turn up Head (H) or Tail (T), the possible outcomes may be:
Head on both coins =(H,H)=HH
Head on first coin and Tail on the other =(H,T)=HT
Tail on first coin and Head on the other =(T,H)=TH
Tail on both coins =(T,T)=TT
Thus, the sample space is S=HH,HT,TH,TT
Clearly, 4 elements are there in the sample space.