C Region contains all the liquids as 0 °C is the freezing point of water (Crystals of water are formed leaving it no more in the liquid state) and 100 °C is the boiling point (The water boils leaving it no more in the liquid state).
When writing an ionic compound formula, a "molecular" form is used. The formula is made with allowance for ion charges. For example, Ca²⁺ and NO₃⁻ ⇒ Ca(NO₃)₂ Al³⁺ and SO₄²⁻ ⇒ Al₂(SO₄)₃