I think the college board was wrong Maybe I am but I don't see how

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Homework Statement

So I solved this problem and I got stuck on B and I don't agree with what the college board says is the right answer or see why my answer is mathematically wrong at all...
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and here's what the college board says please show me how my logic is wrong

5)

(a) two points

CO2

because all contain same number of molecules (moles), and CO2 molecules are the heaviest

Note: total of 1 point earned if CO2 not chosen but same number of molecules (moles) is specified

(b) two points

All are equal

because same temperature, therefore same average kinetic energy

Note: just restatement of "same conditions, etc." does not earn second point

Homework Equations

The Attempt at a Solution

 

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well I feel dumb nevermind =)

 

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if you want to know

PV = nRT
n = (PV)/(RT)

it is the same after all for each ballon

but I still don't see my other question in a different topic is wrong