KCl  is  used  as  salt bridge  because it provides positive K+ ions and negative Cl- ions as the  salt bridge  needs to maintain the neutrality in the system by providing enough negative ions equal to the positive ions during oxidation.

The metals, present below hydrogen in the electrochemical series, cannot liberate hydrogen from the dilute acids.
Among the given metals only Ag is present below hydrogen in electrochemical series, so it does not evolve hydrogen with dil HCl.
Ag −I⁻ dilHCl  ⟶ No reaction

The  standard electrode potentials  are customarily determined at solute concentrations of 1 Molar, gas pressures of 1 atmosphere, and a  standard temperature  which is usually 25 °C i.e, 298 K.

• The tendency of an electrode to lose or gain electrons when it is in contact with its own ions in solution is called electrode potential. 
• Since the tendency to lose electrons means also the tendency to get oxidised, this tendency is called oxidation potential.
• Similarly, the tendency to gain electrons means the tendency to get reduced.
• Hence this tendency is called reduction potential. 

• The standard reduction potential is the tendency for a chemical species to be reduced, and is measured in volts at standard conditions.
• The more positive the potential is the more likely it will be reduced. Hence, A will undergo reduction easily.

Stronger oxidizing agent means more easily it undergoes reduction and thus have greater standard reduction potential.
Remember, Li is the strongest reducing agent and F is the strongest oxidizing agent

• For the reaction Zn + Cu²⁺ →Zn²⁺ + Cu, Zn is oxidized to Zn²⁺ while Cu²⁺ is reduced to Cu
• In a redox reaction, the reactant that loses electrons (is  oxidized ) causes a reduction and is called a reducing agent. In the example above, zinc metal is the reducing agent; it loses two electrons (is  oxidized ) and becomes   Zn²⁺  ion .

The more negative the potential is the more likely the element will be oxidized. Hence, A − is readily oxidized.

The more positive the reduction potential value, the more is the tendency of the element to reduce itself and hence more will be the tendency to accept electrons.

Hence the other element will have more tendency to lose electrons  

Reduction potential means to accept electrons to reduce oneself.
 A + e^- →A^- ∆E_reduction = +ve value
Since, the reduction potential is negative, it means that the reaction will reverse to make ∆E value +ve. So the reaction becomes,
A →A⁺ + e^-  
This becomes oxidation of A. So oxidation of A will be easy.