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

What is the volume in $litres$ of the gas produced at $NTP$ by the reaction of $100 \ g$ of $CaC_2$ with water?
$CaC_2 + 2H_2O \rightarrow Ca(OH)_2 + C_2H_2$

$20.0 \ g$ of a magnesium carbonate sample decomposes on heating to give carbon dioxide and $8.0 \ g$ magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample? $(At. \ wt. \ of \ Mg = 24)$

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

What is the volume in $dm^3$ occupied by $3 \ mol$ of ammonia gas at $STP$?

How many grams of residue is obtained by heating $2.76 \text{ g}$ of silver carbonate (in $\text{ g}$)? (Given: Molar mass of $C$, $O$ and $Ag$ are $12$, $16$ and $108 \text{ g mol}^{-1}$ respectively)