How does gas stoichiometry differ from stoichiometry of solids and liquids\[?\]

Hint: At first you need to understand the difference between the three states of matter solid, liquid and gas. Then try to understand how you calculate the stoichiometry or the number of moles of each one of them for practical purposes. Using this idea you can determine the difference among them.

Complete step-by-step answer:The different states of matter are: solid, liquid and gas.

$\left( a \right)$Now, for solids we can weigh them and hence use the mass of the solid to relate it to the atomic mass unit or $amu$ which can be found in the periodic table. Using $amu$ we can also calculate the number of moles of the solid present in a solution as one $mole$ of an element is equal to $amu$ of that element in $grams$, hence stoichiometry can be known easily.
$\left( b \right)$In case of liquids the stoichiometry i.e. the number of moles of a solute in a solution can be found out by using Molarity, which is given by the expression, $Molarity\, = \,\dfrac{{No.\,of\,moles\,of\,solute}}{{Volume\,of\,solution\,\left( {in\,L} \right)}}$.
This equation can be manipulated in order to obtain the stoichiometry.

$\left( c \right)$Now, solids and liquids have definite volume and hence we can find the stoichiometry easily but for gases, they do not have definite volume hence we use different methods to obtain its stoichiometry.
The two most common methods that are used to find number of moles of gases are:
$ \bullet $ At STP i.e. at a temperature of $273\,K$and a pressure of $760\,torr$ all gases have the same ratio of volume hence a same ratio for number of moles. This is known as Avogadro’s Principle.
$ \bullet $ Also according to Ideal Gas Law$PV = nRT$, where $R$ is the universal gas constant. So if we know the volume, pressure and temperature of the gas we can calculate the number of moles of the gas and hence determine the stoichiometry.

Note:: You should remember the different ways through which you can calculate the stoichiometry of the different states of matter. Do not get confused among them as it may lead to error while calculating the number of moles for solids, liquids and gases.