Some Basic Concepts of Chemistry - Result Question 12 — JEE PYQ Chapterwise

Answer:

Correct Answer: 13. (b)

Solution:

13. The following reaction occur between $\mathrm{S}_2 \mathrm{O}_3^{2-}$ and $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ :

$26 \mathrm{H}^{+}+3 \mathrm{~S}_2 \mathrm{O}_3^{2-}+4 \mathrm{Cr}_2 \mathrm{O}_7^{2-} \longrightarrow 6 \mathrm{SO}_4^{2-}+8 \mathrm{Cr}^{3+}+13 \mathrm{H}_2 \mathrm{O}$

Change in oxidation number of $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ per formula unit is 6 (it is always fixed for $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ ).

Hence, equivalent weight of $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7=\frac{\text { Molecular weight }}{6}$