Distinguish between : Sodium nitrate and sodium sulphite (using dilute sulphuric acid)

State your observation : When moist starch iodide paper is introduced into chlorine gas.

Gas Q turns moist lead acetate paper silvery black. Identify Q. pH of R is 10. What kind of substance is R?

Select the gas that has a characteristic rotten egg smell. [ammonia, ethane, hydrogen chloride, hydrogen sulphide, ethyne]