Two important ores of metals are given below
Malachite `CuCO_(3).Cu(OH)_(2).xH_(2)O`
Carnallite `KCl.MgCl_(2).yH_(2)O`
What is y-x?

Answer

To solve the problem, we need to determine the values of \( x \) and \( y \) from the given chemical formulas of the ores and then calculate \( y - x \).

### Step-by-Step Solution:

1. **Identify the formula of Malachite:**
- The formula of Malachite is given as \( \text{CuCO}_3 \cdot \text{Cu(OH)}_2 \cdot x \text{H}_2\text{O} \).
- Upon examining the formula, we see that there are no water molecules (H2O) present in the structure of Malachite. Therefore, we can conclude that:
\[ x = 0 \]

2. **Identify the formula of Carnallite:**
- The formula of Carnallite is given as \( \text{KCl} \cdot \text{MgCl}_2 \cdot y \text{H}_2\text{O} \).
- Carnallite is known to have 6 water molecules of hydration. Thus, we can conclude that:
\[ y = 6 \]

3. **Calculate \( y - x \):**
- Now that we have both values, we can calculate \( y - x \):
\[ y - x = 6 - 0 = 6 \]

4. **Final Answer:**
- Therefore, the value of \( y - x \) is:
\[ \boxed{6} \]