Why does an aqueous solution of an acid conduct electricity?

Write word equations and then balanced equations for the reaction taking place when –

$(a)$ dilute sulphuric acid reacts with aluminium powder.

$(b)$ dilute hydrochloric acid reacts with iron filings.

$10 \,mL$ of a solution of $NaOH$ is found to be completely neutralised by $8 \,mL$ of a given solution of $HCl$. If we take $20 \,mL$ of the same solution of $NaOH$, the amount of $HCl$ solution (the same solution as before) required to neutralise it will be …… $mL$

Name the sodium compound which is used for softening hard water.

Equal lengths of magnesium ribbons are taken in test tubes $A$ and $B$. Hydrochloric acid $(HCl)$ is added to test tube $A$, while acetic acid $(CH_3COOH)$ is added to test tube $B$. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why ?