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Q.
Among $K, Ca, Fe$ and $Zn$, the element which can form more than one binary compound with chlorine is:
Classification of Elements and Periodicity in Properties
Solution:
A binary compound is one made of two different elements These can be one of each element such as $CuCl$ or $FeO$
These can also be several of each element such a $Fe_{2}O_{3}$ or $SnBr_{4}$
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., $FeCl_{2}, FeCl_{3}$