Baking powder is a mixture of ‘X’ and a mild edible acid such as ‘Y’. When it is heated, ‘Z’ is produced which makes bread and cake soft and spongy X, Y and Z respectively are

Baking powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. When baking powder is heated,CO₂ gas is produced which causes cakes, bread and puff’s to rise, making them soft and spongy 
$\underset{\begin{array}{l}\mathrm{Sodiumhydrogen}\\ \mathrm{Carbonate}\end{array}}{2{\mathrm{NaHCO}}_{3\left(\mathrm{s}\right)}}\stackrel{\mathrm{\Delta }}{\to }\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_{3\left(\mathrm{s}\right)}}+{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$