"Ask the Chemical Formula of Hydrofluoric Acid in Chemistry"

One day, a schoolchild asked Yu Shi: "Dare to ask how to write the chemical formula of hydrofluoric acid?" The teacher said: "Hydrofluoric acid is an aqueous solution of hydrogen fluoride. For hydrogen, the symbol is H; for fluoride, the symbol is F. The chemical formula for the combination of the two is written HF. This is because hydrogen shows + 1 valence and fluorine shows - 1 valence. According to the algebraic sum of the valence, it is zero." Hearing this, the schoolchild suddenly realized and said: "Thank you for your teaching, I know that the chemical formula of hydrofluoric acid is HF."