Question

Which compound among the following has lowest oxidation number of chlorine?

• A. $HCl{O}_4$
• B. $HCl{O}_3$
• C. $HCl$
• D. $HOCl$

Answer 1

The correct option is C $HCl$

Let the oxidation number of chlorine be $x$.

Oxidation number of $H=+1$ and $O=-2$.

(A) $HCl{O}_4$: $1+x+4\times (-2)=0$

$x-7=0$ or $x=7$

(B) $HCl{O}_3$: $1+x+3\times (-2)=0$

$x-5=0$ or $x=5$

(C) $HCl$: $1+x=0$

$x=-1$

(D) $HOCl$: $1+(-2)+x=0$

$x-1=0$ or $x=+1$

Therefore lowest oxidation number of chlorine is -1 in $HCl$.