Question

what is the common name of sodium carbonate​

Answer 1

the common name of sodium carbonate is washing soda

Answer 2

soda ash or washing soda is the common name of sodium carbonate

There are actually two. As you probably know, bases are often refered to as "soda" (baking soda, caustic soda, soda lime, etc.)

The older name is soda ash, referring to its use in soapmaking and the more common name, which is what it is usually sold by, is washing soda, referring to its use in cleaning clothes.