6. Characteristic reactions for four different substances are given below. Arrange the tests in the order of the substances given below.

(i) ${\mathrm{P}}_2{\mathrm{O}}_5$

(ii) ${\mathrm{CO}}_2$

(iii) ${\mathrm{O}}_2$

(iv) ${\mathrm{SO}}_2$

The correct option is B

2341

Explanation:

Substances	Characteristic reactions
(i) Phosphorus Pentoxide ${\mathrm{P}}_2{\mathrm{O}}_5$	Dissolution of ${\mathrm{P}}_2{\mathrm{O}}_5$ in water gives Phosphoric acid, a tribasic acid. $\underset{\mathrm{Phosphorus}\mathrm{pentoxide}}{2{\mathrm{P}}_2{\mathrm{O}}_5}+\underset{\mathrm{Water}}{6{\mathrm{H}}_2\mathrm{O}}\to \underset{\mathrm{Phosphoric}\mathrm{acid}}{4{\mathrm{H}}_3{\mathrm{PO}}_4}$
(ii) Carbon dioxide ${\mathrm{CO}}_2$	It is a non-supporter of combustion but allows active metals such as potassium $\left(\mathrm{K}\right)$, magnesium $\left(\mathrm{Mg}\right)$ continue to burn.
(iii) Oxygen ${\mathrm{O}}_2$	It is a supporter of combustion It turns alkaline pyrogallol from colorless to brown.
(iv) Sulphur dioxide ${\mathrm{SO}}_2$	Sulphur dioxide turns acidified potassium dichromate $\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$ paper to green. The reaction involved is: $\underset{\mathrm{Sulphur}\mathrm{dioxide}}{3{\mathrm{SO}}_2}+\underset{\mathrm{Potassium}\mathrm{dichromate}}{{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7}+\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4}\to \underset{\mathrm{Potassium}\mathrm{sulphate}}{{\mathrm{K}}_2{\mathrm{SO}}_4}+\underset{\mathrm{Chromium}\mathrm{sulphate}\left(\mathrm{green}\right)}{{\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}$

Hence, option (B) is the correct answer. The correct order is 2341.