Which of the following statement regarding Avogadro number is(are) correct?
A. It is `6.023 xx 10^(23)`
B. It is the number of atoms present in exactly `12g` of `C-12` isotope
C. It is the number of atoms present in `1.0` mole on any substance
D. It is the number of atoms of deuterium present in its `2.0g`