Angle of Contact with change in temperature or addition of impurities I read that, 

Angle of contact decrease with the addition of impurities whereas it increases if the temperature is increased

For the explanation of why it increases with increase in temperature, I found out that the surface tension causes the increase in cohesive forces and hence a upward concave. So when temperature rises, surface tension decreases and angle of contact increases. 
Is this explanation correct, and could you explain it in some other way or elaborate about it? 
And I was not able to find why does it decrease with increase in impurities 
Source:

From the Book: Self Study Guide for online BITSAT 2017
 A: Surface tension generally decreases on increasing the temperature i.e adhesion increases. Hence, angle of contact will increase. 
In case of impurities, when a highly soluble impurity like NaCl is added to water, surface tension increases whereas it decreases for sparingly solube (eg: phenol) or insoluble impurities. Hence, angle of contact (on addition of impurities) will decrease or increase accordingly.
Hope this helps!
A: Surface tension increases or decreases depending on the impurity added


*

*highly soluble impurity(e.g.=$\rm NaCl$,$\rm ZnSO_4$,Inorganic Salts):
When they get added into the liquids, adhesive force between liquid molecule and that impurity molecule increases because of the stronger intermolecular force of attraction, hence surface tension increases.

*Less Soluble Impurity(e.g. Soap, Sparingly Soluble Salts)
When they get added to liquids, adhesive force between liquid molecule and that impurity molecule is less than cohesive force among liquid molecule because weaker intermolecular force of attraction among molecules  causes lower surface tension.
