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Molar mass of H₂O = (2 × 1.0) + 16.0 = 18.0 g/mol. Oxygen mass = 16.0 g.

% oxygen = (16.0 ÷ 18.0) × 100 = 88.9%. Percent composition provides the proportion by mass of each element in a compound. ACS objectives highlight applying percent composition to identify compounds, calculate empirical formulas, and analyze experimental data. This skill is crucial for laboratory analysis, environmental testing, and chemical manufacturing.

q = mcΔT = (50.0)(4.18)(60.0) = 12,540 J = 12.5 kJ. Correct option: B.

ACS objectives stress calorimetry applications in enthalpy measurement and thermal energy transfer, critical in thermochemistry and energy management.

[Kr] accounts for 36 electrons. Adding 5s²4d¹⁰5p⁵ gives 53, which is iodine (I). Bromine has 35 electrons, tellurium 52, and xenon 54. ACS objectives stress electron configurations and periodic table placement. This understanding predicts chemical reactivity, periodic trends, and bonding behavior.

The solubility of a substance depends on temperature, pressure (for gases), and solute–solvent interactions, not the color of the solute. ACS objectives emphasize solubility principles, solution equilibria, and predicting precipitation. Understanding solubility is critical in pharmaceuticals, environmental science, and industrial chemistry.

Alpha particles have a +2 charge and high mass, causing intense ionization in a short path but poor penetration (stopped by paper or skin). Beta particles penetrate further but ionize less, while gamma rays penetrate deeply but ionize least per unit distance. ACS objectives emphasize comparing radiation types, their hazards, and their applications in medicine, energy, and safety.