Number of water molecules in washing soda and soda ash respectively are :

<ul> <li><strong>Washing soda</strong> is a hydrated form of sodium carbonate, with the chemical formula Na₂CO₃·10H₂O. This means that each molecule of washing soda contains 10 water molecules.</li><br/> <li><strong>Soda ash</strong> is the anhydrous form of sodium carbonate, with the chemical formula Na₂CO₃. This means that it does not contain any water molecules.</li> </ul> <p>Soda ash is typically produced by heating washing soda to drive off the water molecules. Washing soda can be produced by dissolving soda ash in water and then recrystallizing it.</p> <p>The correct answer is <strong>Option D: 10 and 0</strong>.</p>