Why does dry $HCl$ gas not change the colour of the dry litmus paper?

Which one of the following types of medicines is used for treating indigestion?

Metal compound $A$ reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Why do $HCl$,$HNO_3$,etc.,show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

What will happen if a solution of sodium hydrogencarbonate is heated? Give the equation of the reaction involved.