About aqueous potassium hydroxide and the volume of solution after dissolving?

Concerning the following questions,

A gaseous compound X contains C, H and O only.
100cm^3 of X are mixed with 500cm^3 of oxygen which is known to be in excess. On complete combustion and after cooling back to room temperature, the resulting volume of the reaction mixture is 400 cm^3. On passing the reacting mixture through aqueous potassium hydroxide, the volume is further reduced to 200cm^3.

The answer key says the volume of CO2 produced is 200cm^3 and the volume of O2 consumed is 300cm^3.

Here are my questions:
1) Do aqueous KOH absorbs both water and CO2?

2)I supposed there are CO2, H2O and O2 in the 400cm^3 reaction mixture. Why can it be deduced that there are 200cm^3 CO2 and the 200cm^3 mixture after passing through KOH are all O2?

thanks.