Calgon is used for water treatment. Which of the following statement is NOT true about Calgon?

Calgon is sodium hexametaphosphate with the formula $$Na_6P_6O_{18}$$ (also written as $$(NaPO_3)_6$$). Let us examine each statement.

Option (1): Calgon is a polymeric compound and is water soluble. This is true — sodium hexametaphosphate is a polymeric phosphate that dissolves readily in water.

Option (2): Calgon contains the 2nd most abundant element by weight in the Earth's crust. The most abundant element in Earth's crust by weight is oxygen, and the second most abundant is silicon. Calgon contains sodium (Na), phosphorus (P), and oxygen (O), but does not contain silicon. Therefore, this statement is NOT true.

Option (3): It is also known as Graham's salt. This is true — sodium hexametaphosphate is indeed known as Graham's salt.

Option (4): It does not remove $$Ca^{2+}$$ ion by precipitation. This is true — Calgon sequesters $$Ca^{2+}$$ ions by forming a soluble complex $$[Ca_2(PO_3)_6]^{2-}$$, not by precipitation.

The statement that is NOT true is Option (2).