Practice question

Given: What is the mass percentage of oxygen in K₂Cr₂O₇? (Atomic masses: K = 39, Cr = 52, O = 16) These values define the system as per NCERT data. Formula: Molar mass = (2 × 39) + (2 × 52) + (7 × 16) = 78 + 104 + 112 = 294 g/mol. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Mass of O = 112 g. % O = (112 / 294) × 100 ≈ 38.1%. Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.