To find the mass of the water in the mixture, we can set up the equation based on the total mass of the components involved.
Let \( m_w \) be the mass of the water.
The total mass of the mixture is composed of:
- mass of the water (\( m_w \))
- mass of salt (\( 5.0 \) grams)
- mass of iodine (\( 15.0 \) grams)
We know that the total mass of the mixture is \( 225 \) grams. Therefore, we can write the equation as follows:
\[ m_w + 5.0 , \text{grams} + 15.0 , \text{grams} = 225 , \text{grams} \]
Simplifying this, we combine the mass of salt and iodine:
\[ m_w + 20.0 , \text{grams} = 225 , \text{grams} \]
Now, to find the mass of the water (\( m_w \)), we can subtract \( 20.0 , \text{grams} \) from \( 225 , \text{grams} \):
\[ m_w = 225 , \text{grams} - 20.0 , \text{grams} = 205 , \text{grams} \]
Therefore, the mass of the water is:
A. 205 grams.