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 sets includes all the species that will change the orange colour of $K_2Cr_2O_7$ in acidic medium?

Statement $I$: Sodium hydride can be used as an oxidising agent.
Statement $II$: The lone pair of electrons on nitrogen in pyridine makes it basic.
Choose the $CORRECT$ answer from the options given below:

In the reaction $2Ag + 2H_2SO_4 \to Ag_2SO_4 + 2H_2O + SO_2$,$H_2SO_4$ acts as

Which of the following substances acts as both an oxidizing agent and a reducing agent?