$(a)$ 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?

(N/A) The colour of the solution becomes blue-green and the copper oxide dissolves. The chemical reaction is: $CuO + 2HCl \rightarrow CuCl_2 + H_2O$.
$(b)$ Aqueous solution of $HCl$ dissociates to produce $H^+$ ions,which are responsible for its acidic character. However,glucose $(C_6H_{12}O_6)$ is a covalent compound that does not dissociate into ions in water; therefore,it does not produce $H^+$ ions and fails to show acidic character.