Final answer:
To observe the law of conservation of mass, 179 grams of 2 HCl must be used.
Step-by-step explanation:
To observe the law of conservation of mass, the number of grams of 2 HCl must be equal to the number of grams of Pb(OH)₂ used in the reaction. According to the balanced equation, 2 moles of HCl are produced for every 1 mole of Pb(OH)₂ and the molar mass of Pb(OH)₂ is 241.21 g/mol. Therefore, to calculate the number of grams of HCl needed:
Number of grams of HCl = (2 moles of HCl / 1 mole of Pb(OH)₂) × (molar mass of Pb(OH)₂)
= (2 × 36.5 g/mol) × (241.21 g/mol)
= 175.14 g
Therefore, the correct answer is D) 179. D