1.84 g of a mixture of $\mathrm{CaCO}_3$ and $\mathrm{MgCO}_3$ is strongly heated to get a residue of 0.96 g . The percentage of $\mathrm{CaCO}_3$ in the mixture is

209 g of an element reacts with chlorine to form 315.5 g of its chloride. What is the weight (in g ) of oxygen that reacts with 418 g of same element ?

$$ (\mathrm{Cl}=35.5 \mathrm{u} ; \mathrm{O}=16 \mathrm{u}) $$

Observe the following

I. 0.0063

II. 132.00

III. 1004

The number of significant figures in I, II and III is respectively.

Identify the correct statements from the following.

I. Reaction of hydrogen with fluorine occurs even in dark.

II. Manufacture of ammonia by Haber process is an endothermic reaction.

III. HF is electron rich hydride.