Which of the following statements are correct?

• A

  A sample of CaCO₃ contains Ca = 40%, C= 12%, and O = 48%.If the law of constant composition is true, then the mass of Ca in 10 g of CaCO₃ from another source is 4.0 g.

• B

  12 g of carbon is heated in vacuum and there is no change in the mass, is the best example of the law of conservation of mass.

• C

  Air is heated at constant pressure and there is no change in mass but the volume increases, is the best example of the law of conservation of mass.

• D

   ${\mathrm{SO}}_2$ gas was prepared by (i) heating Cu with conc H₂SO₄, (ii) burning sulphur in oxygen, (iii) reacting sodium sulphate (Na₂SO₄) with  dilute H₂SO₄. It was observed that in each case, S and O combine in the ratio of 1:1. This data illustrates the law of constant composition.