What mass of lif is contained in 18.66 g of a 20.0% by mass solution of lif in water?

Answer is: mass of lithium fluoride is 3,732 grams.
m(solution) = 18,66 g.
ω(solution) = 20% = 20% ÷ 100% = 0,2.
m(LiF) = ?
ω(solution) = m(LiF) ÷ m(solution).
m(LiF) = ω(solution) · m(solution).
m(LiF) = 0,2 · 18,66 g.
m(LiF) = 3,732 g.

The simplest way to use the periodic table to identify an element is by looking for the element's name or elemental symbol. The periodic table can be used to identify an element by looking for the element's atomic number. The atomic number of an element is the number of protons found within the atoms of that element.