In preparing a salt bridge we sue `KCl` because

Options

A. the hydration power of `K^(+)` and `Cl^(-)` ions are the same
B. the electropositive character of `K` and electronegative character of `Cl^(-)` are comparable
C. the equivalent conductance of `K^(+)` and `Cl^(-)`are nearly the same at infinte dilution
D. the sizes of the `K^(+)` and `Cl^(-)` are almost equal

Answer

C

Explanation

Flow of an electric current requires unbroken contacts all over the circuit. For providing contacts between solution of electrolytes, solutions of inert electrolytes can be used. Inert electrolytes are those whose ions are not involved in the electrochemical chages nor do they react chemically with the electrolytes electrically connecteed by them. for example, we can't `Ba` salt bridge in a Daniell cell as they will precipitate out sulphate ions.
The link electrolyte solutions are usually of salts and hence the name salt bridge for them. Salt solutions used for bridg-ing are taken at higher concentrations than the electrolyte solutions linked by them.
The most often used salt bridges are `KCl` and `KNO_(3). NH_(4)NO_(3)` is also used sometimes. The equivalent conductances of `K^(+)` and `Cl^(-)` are nearly the same at infinite dilution because they have nearly the same ionic mobility and trasport numbers. The ionic mobility of an ion in solution is the velocity with which an ion would move under potential gradient of `1 V m^(-1)` in a solution. Mathematically
Ionic mobility `= ("Ionic velocity" (ms^(-1)))/("Potential gradient" (Vm^(-1)))`
Transport number (or transference number) of an ion indicated by the symbol `t_(+)` or `t_(-)` is the fraction of the total current carried by an ion. Mathematically
`t_(+) = (i_(+))/(i_(+)+i_(-))` and `t_(-) = (i_(-))/(i_(+)+i_(-))`
`t_(+)+t_(-) = 1`
The bridge is made with an agar gel. This arrangement pre-vents mechanical flow of solutions through the bridge, but provides free path for electrical migration of ions to maintain an electrical current through the involved electrolytes.