In a basic aqueous solution,if the concentration of $[OH^-]$ increases,what happens to the $pOH$?

Salt $A$,commonly used in bakery products,on heating gets converted into another salt $B$,which itself is used for the removal of hardness of water,and a gas $C$ is evolved. The gas $C$,when passed through lime water,turns it milky. Identify $A$,$B$,and $C$.

Which of the following is a mineral acid?

Write balanced chemical equations for the following:
$(a)$ Calcium carbonate reacts with hydrochloric acid.
$(b)$ Calcium oxychloride reacts with hydrochloric acid.
$(c)$ Sodium hydroxide reacts with zinc.

When soap is scrubbed on a stain of curry on a white cloth,why does it become reddish-brown,and why does it turn yellow again when the cloth is washed with plenty of water?

To protect against tooth decay,we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is: