AgX has rock-salt structure, density 6477 kg/m³ and cell edge 577.5 pm. Ag atomic weight is 107.87 g/mol. Find atomic weight of X in g/mol, to 2 decimals.
Rock salt has four AgX formula units per unit cell. Thus $M_{AgX}=\rho a^3N_A/4$, using consistent units. With ρ = 6.477 g/cm³ and a = 5.775×10⁻⁸ cm, M ≈ 187.81 g/mol. Subtract Ag: MX ≈ 79.94 g/mol, identifying the bromide-scale atomic weight and lying in the original 79–81 interval.
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