Question

How calculate this ?

Answer 1

Would it not be `B`?

Explanation:

Look at your stoichiometry. All the reagents, reactants, and products, are in the gaseous state...

`2CO(g) + O_2(g) rarr 2CO_2(g)`

And because under conditions of equivalent pressure and temperature, such as are invoked HERE....VOLUME is proportional to the number of moles (this is old Avogadro's gas law...`V_"volume of gas"propn_"moles of gaseous particles"`

And your equation explicitly says, that TWO volumes of `CO` react with ONE volume of dioxygen to give TWO VOLUME of `CO_2`. Capisce? The stoichiometry is there in front of you.

And so if have a `40*cm^3` volume of `CO` equivalence requires a `20*cm^3` volume of `O_2` to give a `40*cm^3` volume of `CO_2`, the product.

All of this is an example of stoichiometry. When you make or receive change for a cash transaction I suspect that you are seldom short-changed. Why? Because you are trained from an early age to handle money, to assess stoichiometric equivalence. And we are doing precisely the same thing here...