Baking soda is chemically represented by$\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_?$

$0$

A$.$ Na$2$CO$3$

B$.$ NaHCO$3$

C$.$ Na$2$CO$3.$H$2$O

D$.$ Na$2$CO$3\mathrm{.}10$H$2$O