Answer
The correct answer is (b)
Work Step by Step
When the reaction occurs, $KCl$ ans $Sr(OH)_2$ are formed. $K^+$ and $Cl^-$ are present on both sides of the equation, so they are spectator ions. $Sr(OH)_2$ is solid so it is not represented as dissociated ions. So, the net ionic equation is the one given in option (b)