Question

Why is Carbon 12 isotope used as a standard reference for measuring atomic mass?

Answer 1

Earlier scientist used hydrogen as refernce, but by doing so atomic mass od most eemnts came out to be fractional. So the refrence was changed to oxygen-16. But the ecientist picked up natural occuring oxygen which is a mixture of O-16, O-17 and O-18. This led to confusion.
So they changed the refrence to Carbon-12 .
The adavantage of using this refernce was that by taking it as refernce the atomic mass of all other elements were found exactly.
Also, Carbon-12’s atomic mass could be measured particularly accurately compared to the other elements on the periodic table.