What is the relative formula mass of calcium hydroxide, Ca(OH)2? (Ar: Ca = 40, O = 16, H = 1)

Answer and explanation

Correct answer: A. 74

  1. Step 1: Ca = 40.
  2. Step 2: The brackets contain O + H = 17, and there are two of them: 34.
  3. Step 3: 40 + 34 = 74.
Answer
74.
Why not the others: 57 counts only one OH group, 41 counts only one hydrogen and no oxygen, and 72 counts the two oxygen atoms but leaves out both hydrogen atoms.

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