dear ankur
Na2CO3 is a strongly basic salt, while NaHCO3 is a weakly basic salt
One easy way to distinguish between them is to make a solution of each one and test their pH. The NaHCO3 will be about pH = 8. The Na2CO3 will show a pH of about 11 - 12
Another easy way is to heat the two compounds. NaHCO3 will decompose at a relatively low temperature yielding CO2(g) and H2O(g). The H2O will condense on a cool surface and can be identified that way. Na2CO3 requires much more heat to decompose and will only give off CO2(g).
hope it clears
regards