$A$ spherical ball of radius $7 \ cm$ contains $56 \ w\%$ iron. Find out the number of moles of iron present approximately in the ball (in $.1$)? $(d = 1.4 \ g \ cm^{-3}; \text{atomic mass} = 56 \ g \ mol^{-1})$

If one wants to make methanol out of synthesis gas,what should be the ratio of the gaseous components in the synthesis gas?

Suppose a cooking gas cylinder contains $11.2 \, kg$ of isobutane. The thermochemical equation for the combustion of butane is given below:
$C_4H_{10}(g) + \frac{13}{2} O_2(g) \to 4CO_2(g) + 5H_2O(\ell); \Delta H = -2658 \, kJ$
If a family requires $15000 \, kJ$ of energy per day for cooking,how many days will the cylinder last?

Chlorine is prepared in the laboratory by treating manganese dioxide $(MnO_{2})$ with aqueous hydrochloric acid according to the reaction
$4HCl_{(aq)} + MnO_{2(s)} \rightarrow 2H_{2}O_{(l)} + MnCl_{2(aq)} + Cl_{2(g)}$
How many grams of $HCl$ react with $5.0\ g$ of manganese dioxide?

The solution of sulphuric acid contains $80\%$ by weight $H_2SO_4$. The specific gravity of this solution is $1.71$. Its normality is about:

$2.76 \, g$ of silver carbonate on being strongly heated yields a residue weighing $..........$ $g$.