Of the molecules pf3 and pcl3, which has bonds that are more polar? hints

We know that the greater the difference is in electronegativity between the atoms which holds the molecule, the greater the polarity is the bonds between them. 

Since we know that F has the highest electronegativity among all the elements,  therefore PF3 has more polar bonds than PCl3. 

i do not get it   at all

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.