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JEE CHEMISTRY MCQ: REDOX REACTIONS

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Analyzing +4 | -1

Assertion: Oxidation number of carbon in

\mathrm{HCHO}

is zero.

Reason:

\text{HCHO}

formaldehyde, is a covalent compound.

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Correct option: B

Assertion is true, Reason is true and Reason is not correct explanation for Assertion

Option B is correct because both the assertion and reason are true, but the reason is not the correct explanation for the assertion. The oxidation number of carbon in HCHO is zero, and HCHO is a covalent compound, but the latter doesn't explain the former.

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The oxidation number of

\mathrm{H}

in sodium hydride is A reagent, which can decrease the oxidation number of an element, is called Consider the following decomposition reaction

2 \mathrm{KClO}_3 \longrightarrow 2 \mathrm{KCl}+3 \mathrm{O}_2

In the above reaction, Assertion (A):

\mathrm{HNO}_3

acts as oxidizing agent.

Reason (R): Oxidation no. of nitrogen is +5, no increase in oxidation no. beyond +5 can occur. The oxidation no. of

\mathrm{HNO}_3

can only decrease. Assertion :- Bromide ion is serving as a reducing agent in the reaction.

\mathrm{MnO}_4^{-}(\mathrm{aq})+\mathrm{Br}^{-}(\mathrm{aq})+\mathrm{H}_2 \mathrm{O} \longrightarrow 2 \mathrm{MnO}_2(\mathrm{aq})+\mathrm{BrO}_3^{-}(\mathrm{aq})+2 \mathrm{OH}^{-}(\mathrm{aq})

Reason :- Oxidation number of

\mathrm{Br}

-1

+5.

A substance, that by its sharp colour change indicates the completion of reaction is known as :