Question

What are the source of error in determination of boiling point and melting point

Answer 1

 purity of the substance is usually the main error (for example: water with impurities will have m.p. less than 273K or 0 degree celcius while it's b.p. will be greater than 373K or 100 degree celcius). 
-> air/ room temperature (it takes longer to cook in mountains and shorter at beaches) 
-> parallax error (error by determining the meniscus of the thermometer) 
and many more..