A television uses plasmas
Answer : The reaction is endothermic.
Explanation :
Formula used :

where,
= change in temperature = 
Q = heat involved in the dissolution of KCl = ?
m = mass = 0.500 + 50.0 = 50.5 g
c = specific heat of resulting solution = 
Now put all the given value in the above formula, we get:


The heat involved in the dissolution of KCl is positive that means as the change in temperature decreases then the reaction is endothermic and as the change in temperature increases then the reaction is exothermic.
Hence, the reaction is endothermic.
The answer is going to be mercury