The correct answer is option 3, Sodium Carbonate. Washing Soda is the common name for Sodium Carbonate, which is a chemical compound that is commonly used as a cleaning agent and laundry detergent.

Option 1, Calcium Carbonate, is incorrect. Calcium Carbonate is a different chemical compound commonly known as limestone or chalk. It is often used in the production of cement and as a dietary supplement.

Option 2, Magnesium Carbonate, is also incorrect. Magnesium Carbonate is a chemical compound that is often used in the production of medicines, antacids, and as a drying agent. It is not commonly known as Washing Soda.

Option 4, Potassium Carbonate, is incorrect as well. Potassium Carbonate is a chemical compound that is often used in the production of glass, soaps, and fertilizers. It is not commonly known as Washing Soda.

Therefore, the correct common name for Washing Soda is Sodium Carbonate.