Which of the following compounds does not contain a peroxide ion?

When $SO_2$ is passed through an acidic solution of potassium dichromate,chromium sulphate is formed. What is the change in the oxidation state of chromium?

What are the respective oxidation states of sulphur atoms numbered $1$ to $4$ in the tetrathionate ion $(S_4O_6^{2-})$ shown below?

The oxidation number of sulphur is $-4$ in

What is the oxidation state of $Fe$ in $Fe_{0.94}O$?

Oxidation state of manganese in potassium permanganate is: