# The following is the percentage composition of a compound. $Na = 16.08 \%, C = 4.19 \%, O = 16.78 \%$ and $H_2O = 62.95 \%$ . Its molecular formula is
$(a)\;Na_2CO_3 \\(b)\;Na_2CO_3.H_2O \\(c)\;Na_2CO_3.10H_2O\\(d)\;Na_2CO_3.5H_2O$