Definition of gas : Something which does not have definite volume or shape.
But , we can measure the volume of gas , say, 1 mole of gas contains 22.4l of gas.
How is this possible.?

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Solution

The definition of gas says that gases does not have "definite volume". It is true because gases takes the volume of container in which it is kept.
Here in your second statement "1 mole of gas contains 22.4l of gas".
Generally we specify two parameters (pressure and temperature) to explain a gas. In this case the number of moles of gas is fixed. It's temperature and pressure parameters are also restricted. So, we are getting the value of volume occupied by the gas.
Now suppose at same temperature and pressure , if you take a gas (unknown amount) and keep it in two different container having different volumes. Then how can you tell the volume of gas in each container? by measuring the volume of container only.
So, basically the gases does not have definite volume.

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According to Avogadro's Law, "Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules". But how is this statement correct? How do we know that equal number of molecules are present in two gases taken in equal volumes?

Even if we consider equal volumes of any two gases(let's consider two gases for example) contain equal number of molecules, if we have the two gases in two containers of same volumes, we can add more gas to any one container and increase the density of the gas inside the container. In that case, the volume of the gas remains equal to the volume of the container but the number of gas molecules inside the container has increased and there is no chage to the number of molecules of the other gas we took inside a similar container. So now we have equal volumes of two gases but we have increased the number of molecules of one gas so now how can we say that the equal volumes of these two gases contain equal number of molecules?

If we take equal number of molecules of two gases and contain one of the gas in a container of some volume and the other gas in a container of a different volume, we will have unequal volumes of two gases having equal number of particles.

So how is Avogadro's Law explained?

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Definition of gas : Something which does not have definite volume or shape.But , we can measure the volume of gas , say, 1 mole of gas contains 22.4l of gas.How is this possible.?

Definition of gas : Something which does not have definite volume or shape.
But , we can measure the volume of gas , say, 1 mole of gas contains 22.4l of gas.
How is this possible.?