Three coins are tossed.

$\therefore$ The sample space =$2^3=8$ possible outcome

$S=\{HHH,HHT,HTH,HTT,THH,THT,TTH,TTT\}$

Let A be the event ,"No heads" shown

$\therefore A=\{TTT\}$

Let B be the event ,"Atleast one head"

$\therefore B=\{HHH,HHT,HTH,HTT,THH,THT,TTH\}$

$\therefore A \cap B=\phi$ and $A \cup B=S$

$\therefore$ A and B are mutually exclusive and exhaustive.