To determine how many moles of KCl would be dissolved in 4 liters of water to make a 2 M solution, let's proceed with the following steps:
1. Understand the given data:
- Volume of water: [tex]\( 4 \)[/tex] liters
- Molarity of the solution: [tex]\( 2 \)[/tex] M (moles per liter)
2. Recall the formula for molarity (M):
[tex]\[ \text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}} \][/tex]
3. Rearrange the formula to solve for moles of solute:
[tex]\[ \text{moles of solute} = \text{Molarity (M)} \times \text{liters of solution} \][/tex]
4. Plug in the values:
[tex]\[ \text{moles of KCl} = 2 \, \text{M} \times 4 \, \text{L} \][/tex]
5. Perform the multiplication:
[tex]\[ \text{moles of KCl} = 8 \, \text{moles} \][/tex]
Therefore, the number of moles of KCl that would be dissolved in 4 liters of water to make a 2 M solution is:
[tex]\[ \boxed{8 \, \text{moles}} \][/tex]
The correct answer is [tex]\( \text{B. } 8 \, \text{moles} \)[/tex].
