Question

Why is carbon chosen as a base standard to calculate the mass of other elements and not any other element for atomic mass?

Answer 1

$\huge\mathfrak\red{Hey\:Mate}$

Physicists picked the pure isotope Oxygen-16, because they tended to make their measurements on the basis of mass spectrometry. Instead of using either Hydrogen, or Oxygen as the standard, the isotope of Carbon with 6 protons and 6 neutrons in its nucleus (Carbon-12) was given a mass of exactly 12.

Answer 2

$\huge\mathfrak\red{heya\:Mate}$

because it is a pure isotopes having mass of 12 u.