Among K, Ca, Fe and Zn, the element which can form more than one binary compound with chlorine is

A binary compound is one made of two different elements.

These can be one of each element such as $\mathrm{CuCl} \mathrm{or} \mathrm{FeO}$ 

These can also be several of each element such as ${\mathrm{Fe}}_2{\mathrm{O}}_3\mathrm{or}{\mathrm{SnBr}}_4.$

Metals which have variable oxidation number can form more than one type of binary compounds like Fe shows the oxidation state +2 and +3. Hence it forms two types of binary compounds, e.g., ${\mathrm{FeCl}}_2,{\mathrm{FeCl}}_3.$