The concentration of the solution is 5.0 molar, which is 5.0 mole/L. So in the 1.0 L of 5.0 molar KF salt solution, the moles of KF is 5.0molar*1.0L=5.0 mole. The molecular weight of KF is given in the question as 58.10 gram/mole, so the grams of KF is 58.10 gram/mole * 5.0 mole = 290.5 gram.
