Which one of the following materials is present in a guard tube (drying tube) that is used for preparation of HCl gas?

When we heat lead nitrate [P(NO₃)₂] in a boiling tube, we observe the emission of brown fumes. Which one of the following is the brown gas?

Which one of the following is not an oxidation reaction?

Which one of the following compounds is used in 'black and white' photography?

Which one of the following is not an example of an oxidation reaction?

Which one among the following is an example of oxidation reaction?