Which absorbs gaseous carbon dioxide most effectively?

Solid $\mathrm{KOH}$ absorbs gaseous carbon dioxide most effectively.

Solution of potassium hydroxide absorbs$C{O}_2$ and $S{O}_2$. Potassium hydroxide, sometimes known as caustic potash, is an inorganic chemical with the formula $\mathrm{KOH}$ . $KHC{O}_3$, which is still soluble in the solution, is created when excess $C{O}_2$is absorbed by $\mathrm{KOH}$ .