Carbon dioxide can be detected by the lime water test.

The formation of the oxide ion ${\mathrm{O}}^{2-}\left(\mathrm{g}\right)$ requires first, an exothermic and then, an endothermic step as shown below:

$\mathrm{O}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}={\mathrm{O}}^{-}\left(\mathrm{g}\right); ∆{\mathrm{H}}^{\mathrm{o}}=-142\mathrm{ }\mathrm{kJ}\mathrm{ }{\mathrm{mol}}^{-1}$

${\mathrm{O}}^{-}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}={\mathrm{O}}^{2-}\left(\mathrm{g}\right),\mathrm{ }∆{\mathrm{H}}^{\mathrm{o}}=844\mathrm{ }\mathrm{kJ}\mathrm{ }{\mathrm{mol}}^{-1}$. This is because

Complete the given analogy:

Fruits : protect seeds :: leaves : _____.

(Mention the process)

Translate the following statements into chemical equation and then balance these
Calcium oxide reacts with water to give calcium hydroxide and release heat.

What is the difference between endothermic and exothermic reactions?