The ratio of the mass percentages of ‘C & H’ and ‘C & O’ of a saturated acyclic organic compound ‘X’ are 4 : 1 and 3 : 4 respectively. Then, the moles of oxygen gas required for complete combustion of two moles of organic compound ‘X’ is ________.

10.30 mg of O₂ is dissolved into a liter of sea water of density 1.03 g/mL. The concentration of O₂ in ppm is__________.

The hardness of a water sample containing 10^–3 M MgSO₄ expressed as CaCO₃ equivalents (in ppm) is ______.
(molar mass of MgSO₄ is 120.37 g/mol)

The molarity of HNO₃ in a sample which has density 1.4 g/mL and mass percentage of 63% is _____.
(Molecular Weight of HNO₃ = 63)