Which colourless gas evolves,when $NH_4Cl$ reacts with zinc in a dry cell battery?

Depict the galvanic cell in which the reaction $Zn_{(s)} + 2Ag^{+}_{(aq)} \rightarrow Zn^{2+}_{(aq)} + 2Ag_{(s)}$ takes place,further show:
$(i)$ which of the electrode is negatively charged,
$(ii)$ the carriers of the current in the cell,and
$(iii)$ individual reaction at each electrode.

Consider the galvanic cell: $A_{(s)} | A_{(aq)}^{+2} || B_{(aq)}^{+} | B_{(s)}$. If the $EMF$ of the cell is positive,identify the correct cell reaction from the following.

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:

The efficiency of a fuel cell is given by

Copper cannot replace $.....$ from its solution.