Which of the following is not a reducing agent?

Starch iodide paper is used to test for the presence of .........

When acidified $K_2Cr_2O_7$ solution is added to $Sn^{2+}$ salt,then $Sn^{2+}$ changes to . . . . . . .

Which of the following mixtures is chromic acid?

The oxide which cannot act as a reducing agent is

While sulphur dioxide and hydrogen peroxide can act as oxidising as well as reducing agents in their reactions,ozone and nitric acid act only as oxidants. Why?