Despite the fact that the partial pressure difference is so much smaller for co2, why is there as much co2 exchanged between the alveoli and blood as there is o2, ?

This is due to the solubility of CO₂ in blood is more than the solubility of Oxygen in blood 

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

It has to be b i hope this