4.0 g of a mixture containing $\mathrm{Na}_2 \mathrm{CO}_3$ and $\mathrm{NaHCO}_3$ is heated to 673 K . Loss in mass of the mixture is found to be 0.62 g . The percentage of sodium carbonate in the mixture is

0.43 g of a metal of valence 2 was dissolved in 50 mL of $0.5 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}$ solution. The unreacted acid required 14.2 mL of 1 M NaOH solution for neutralisation. The atomic weight of the metal is

The incorrect rule regarding the determination of significant figures is

12 g of an element reacts with 32 g of oxygen. What is the equivalent weight of the element ?