(a) What happens chemically when quicklime is added to water? Write chemical equation of the reaction involved.
(b) What is 'Baking Powder'? How does it make the cake soft and spongy?

(a) When quicklime or calcium oxide(CaO) is added to water then it reacts vigorously with water and forms slaked lime or calcium hydroxide(Ca(OH)₂). This reaction is highly exothermic and a large amount of heat is released in the process. The chemical reaction involved is as follows:

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}\left(\mathrm{OH}{)}_2\right(\mathrm{aq})$

(b) Baking powder is a mixture of baking soda(sodium hydrogen carbonate) and a solid, edible acid such as tartaric acid or citric acid. When baking powder is mixed with water, the sodium bicarbonate reacts with tartaric acid to produce carbon dioxide gas. The carbon dioxide gas gets trapped in the wet dough made for baking a cake or bread and then bubbles out slowly. Which makes the cake or bread soft and spongy.