Ca(s) + CO2(g) -----> CaCO3(s)
What mass of CO2 could be absorbed by 1.25g of CaO?

What volume would this CO2 occupy at STP?

(Note that in your equation, you typed Ca instead of CaO)

Find the relative mass of CaO.
Thus, find the number of moles of CaO present in 1.25 g of CaO.
Using your equation, deduce the number of moles of CO2 required.
At stp, 1 mole of gas occupies 22.4 L or 22.4 dm^3. You have the numberof moles of CO2, find the volume!