In a dry cell,which element acts as the negative electrode?

In the cell $Zn | Zn^{2+} || Cu^{2+} | Cu$,the negative electrode is

$A$ saturated solution of $KNO_3$ with agar-agar is used to make a 'salt-bridge' because

The electrochemical cell is set up as follows: $Pt (H_2, 1 \, atm) | HCl (0.1 \, M) || \text{Acetic Acid} (0.1 \, M) | (H_2, 1 \, atm) Pt$. The $E.M.F.$ of the cell is not zero because:

$A$ hypothetical electrochemical cell is shown below.
$A \,|\, A^{+} \,(x \ M)\, ||\, B^{+} \,(y \ M)\, |\, B$
The $emf$ measured is $+ 0.20 \ V.$ The cell reaction is

Which of the following mixtures is used as an electrolyte paste in a mercury cell?