Question

give me solution
please help

Answer 1

The very first point that is to be given importance here is that it is not specified that it is at standard temperature and pressure(STP).

but it is given that all the 3 gas jars are kept at some constant temperature and pressure.

So, 1 mole of any gas (in this case) do not occupy 22.4 litres but some other particular constant volume which we will have to find out.

Given that,
1st jar contains 2L of CO2
2nd jar conatins 5L of H2
3rd jar contains 7L of O2

Also it is said that 2.4 x 10²² molecules of CO₂ in first jar occupy 2 litres
and so we get 1 mole(6 x 10²³ molecules of CO₂) occupies 25 litres

So, by the above statement we can conclude that 1 mole of any gas at that given temperature and pressure occupies 25 litres

25 litres of hydrogen contain 1mole(6 x 10²³ molecules) of hydogen gas.
so 5 litres of hydrogen in 2nd jar has 0.2 moles(1.2 x 10²³ molecules of H₂) 

25 litres of oxygen contain 1mole( 6 x 10²³ molecules) of oxygen gas.
so 7 litres of oxygen in 3rd jar has 0.28moles( 1.68 x 10²³ molecules of O₂) 

:)