Chemical formula of washing soda is ________ .

Na₂CO₃ . 10H₂O

The correct answer is option 1. Na₂CO₃. 10H₂O.

Washing soda, also known as sodium carbonate decahydrate, has the chemical formula \(Na_2CO_3 \cdot 10H_2O\). Let's break down this formula:

1. \(Na_2CO_3\):  This represents sodium carbonate, a compound consisting of two sodium ions (\(Na^+\)) and one carbonate ion (\(CO_3^{2-}\)).

2. \(10H_2O\): This indicates ten water molecules (water of crystallization), which are associated with the compound in its crystalline form.

So, the complete formula \(Na_2CO_3 \cdot 10H_2O\) signifies that one molecule of washing soda contains two sodium ions, one carbonate ion, and ten water molecules. The water molecules are part of the crystal structure of washing soda and can be removed by heating, converting it to anhydrous sodium carbonate (\(Na_2CO_3\)). Washing soda is commonly used in laundry as a water softener and in various household cleaning applications.