On balancing the given redox reaction a… - NEET UG 2023 Chemistry PYQ

NEET UG 2023 — Chemistry Physical Chemistry

2023mcqmedium

On balancing the given redox reaction

$a{\mathrm{Cr}}_{2}{O}_{7}^{2-}+{\mathrm{bSO}}_{3}^{2-}(\mathrm{aq})+{\mathrm{cH}}^{+}(\mathrm{aq})\overset{}{\rightarrow }2{\mathrm{aCr}}^{3+}(\mathrm{aq})+{\mathrm{bSO}}_{4}^{2-}(\mathrm{aq})+\frac{c}{2}{H}_{2}O(l)$

The coefficients $a,b,c$ are found to be respectively

Official previous-year question

Held on 30 Apr 2023 · Verified 9 Jul 2026.

Options

A
$8,1,3$
B
$1,3,8$
C
$3,8,1$
D
$1,8,3$

Did you get this right?

Solution

Reduction Half reaction : ${\mathrm{Cr}}_{2}{{O}_{7}}^{2-}+6{e}^{-}\rightarrow 2{\mathrm{Cr}}^{3+}$

Oxidation Half reaction :

${{\mathrm{SO}}_{3}}^{2-}\rightarrow {{\mathrm{SO}}_{4}}^{2-}+2{e}^{-}\times 3$

Overall reaction :

${\mathrm{Cr}}_{2}{{O}_{7}}^{2-}+3{{\mathrm{SO}}_{3}}^{2-}\rightarrow 2{\mathrm{Cr}}^{3+}+3{{\mathrm{SO}}_{4}}^{2-}$

To balance $‘O’$ atoms, adding ${H}_{2}O$ on LHS

${\mathrm{Cr}}_{2}{{O}_{7}}^{2-}+3{{\mathrm{SO}}_{3}}^{2-}\rightarrow 2{\mathrm{Cr}}^{3+}+3{{\mathrm{SO}}_{4}}^{2-}+4{H}_{2}O$

To balance $‘H’$ atoms, adding ${H}^{+}$ on RHS

${\mathrm{Cr}}_{2}{{O}_{7}}^{2-}+3{{\mathrm{SO}}_{3}}^{2-}+8{H}^{+}\rightarrow 2{\mathrm{Cr}}^{3+}+3{{\mathrm{SO}}_{4}}^{2-}+4{H}_{2}O$

Therefore, $a=1,b=3,c=8$ .

Your note

NEET UG Physical Chemistry in other years

Physical Chemistry 2026 Physical Chemistry 2025 Physical Chemistry 2024 Physical Chemistry 2022 Physical Chemistry 2021 Physical Chemistry 2020 Physical Chemistry 2019 Physical Chemistry 2018 Physical Chemistry 2017 Physical Chemistry 2016 Physical Chemistry 2015 Physical Chemistry 2014

More NEET UG Physical Chemistry questions

For the reaction 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH = -198 kJ. Which condition favours forward reaction?

2026medium

The unit of rate constant for a first-order reaction is:

2026easy

Among the following choose the ones with equal number of atoms. A. 212 g of $\mathrm{Na}_2 \mathrm{CO}_3(\mathrm{~s})$ [molar mass $=106 \mathrm{~g}$ ] B. 248 g of $\mathrm{Na}_2 \mathrm{O}$ (s) [molar mass $=62 \mathrm{~g}$ ] C. 240 g of $\mathrm{NaOH}(\mathrm{s})$ [molar mass $=40 \mathrm{~g}]$ D. 12 g of $\mathrm{H}_2(\mathrm{~g})$ [molar mass $=2 \mathrm{~g}$ ] E. 220 q of $\mathrm{CO}_2(\mathrm{q})$ [molar mass $\left.=44 \mathrm{~g}\right]$ Choose the correct answer from the options given below:

2025medium

For the reaction $\mathrm{A}(\mathrm{g}) \rightleftharpoons 2 \mathrm{~B}(\mathrm{~g})$, the backward reaction rate constant is higher than the forward reaction rate constant by a factor of 2500 , at 1000 K . [Given : $\mathrm{R}=0.0831 \mathrm{~L} \mathrm{~atm} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$ ] $\mathrm{K}_{\mathrm{p}}$ for the reaction at 1000 K is

2025medium

The standard heat of formation, in $\mathrm{kcal} / \mathrm{mol}^{\text {of }} \mathrm{Ba}^{2+}$ is : [Given : standard heat of formation of $\mathrm{SO}_4^{2-}$ ion (aq) $=-216 \mathrm{kcal} / \mathrm{mol}$, Standard heat of crystallisation of $\mathrm{BaSO}_4(\mathrm{~s})=-4.5 \mathrm{kcal} / \mathrm{mol}$, standard heat of formation of $\left.\mathrm{BaSO}_4(\mathrm{~s})=-349 \mathrm{kcal} / \mathrm{mol}\right]$

2025medium

View all Physical Chemistry questions

Keep practicing Physical Chemistry

Work through every NEET UG Physical Chemistry PYQ, year by year.

Browse all Chemistry topics

Options

Did you get this right?

Solution

Your note

NEET UG Physical Chemistry in other years

More NEET UG Physical Chemistry questions

Other Chemistry topics for NEET UG

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry