<u>Answer:</u> The mass of calcium hydroxide that are present in the solution is 0.3256 grams.
<u>Explanation:</u>
To calculate the moles of a solute, we use the equation:

We are given:
Volume of hydrochloric acid = 42.7mL = 0.0427 L (Conversion factor: 1 L = 1000 mL)
Molarity of the solution = 0.208 moles/ L
Putting values in above equation, we get:

For the given chemical reaction:

By Stoichiometry of the reaction:
2 moles of hydrochloric acid reacts with 1 mole of calcium hydroxide.
So, 0.0088 moles of hydrochloric acid will react with =
of calcium hydroxide.
To calculate the mass of calcium hydroxide, we use the equation:

Moles of calcium hydroxide = 0.0044 moles
Molar mass of calcium hydroxide = 74 g/mol
Putting values in above equation, we get:

Hence, the mass of calcium hydroxide that are present in the solution is 0.3256 grams.