A sample of crystalline soda (A) with a mass of 1.287 g was allowed to react with excess hydrochloric acid and 100.8 mL of gas was liberated at STP. How many molecules of water in relation to one molecule of $$\mathrm{Na_2CO_3}$$ are contained in the sample of soda? Relative atomic masses are Na = 23, H = 1, C = 12 and O = 16.

A

5

B

6

C

4

D

10