Whose acid-base theory can be applied to aqueous and non-aqueous solutions?

One of the constituents of baking powder is sodium hydrogencarbonate, the other constituent is

$(a)$ What will you observe when dilute hydrochloric acid is added to a small amount of copper oxide in a beaker?
$(b)$ Aqueous solution of $HCl$ shows acidic character. But the aqueous solution of glucose fails to do so. Why?

$(a)$ If we take hydrochloric acid and acetic acid of the same concentration,which one will produce a lower $H^{+}$ ion concentration? Out of the two,which one is a weak acid?
$(b)$ If someone is suffering from acidity,which of the following would you suggest to cure it: vinegar,orange juice,or baking soda solution? Give a reason for your answer.

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?

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