Oxidation number and balancing redox reactions — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Oxidation is associated with

• A. an increase in oxidation number
• B. a decrease in oxidation number
• C. no electron transfer
• D. a decrease in valence electrons only with no redox change

Question 2 · difficulty L2 · understanding

In the reaction of potassium dichromate, potassium chloride and sulfuric acid (conc.), the oxidation state of the chromium in the product is $$(+)$$ _________.

Question 3 · difficulty L2 · understanding

See the following chemical reaction: $$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{XH}^{+}+6 \mathrm{~F}_{e}^{2+} \rightarrow \mathrm{YCr}^{3+}+6 \mathrm{~F}_{e}^{3+}+\mathrm{Z} \mathrm{H}_{2} \mathrm{O}$$ The sum of $$\mathrm{X}, \mathrm{Y}$$ and $$\mathrm{Z}$$ is ___________

Question 4 · difficulty L2 · understanding

The sum of oxidation state of the metals in $$\mathrm{Fe}(\mathrm{CO})_{5}, \mathrm{VO}^{2+}$$ and $$\mathrm{WO}_{3}$$ is ___________.

Question 5 · difficulty L2 · understanding

In ammonium - phosphomolybdate, the oxidation state of Mo is + ___________

Question 6 · difficulty L2 · understanding

Sum of oxidation states of bromine in bromic acid and perbromic acid is ___________.

Question 7 · difficulty L2 · understanding

The oxidation state of phosphorus in hypophosphoric acid is + _____________.

Question 8 · difficulty L2 · understanding

Dichromate ion is treated with base, the oxidation number of Cr in the product formed is ___________.

Question 9 · difficulty L2 · understanding

Given below are two statements: Statement (I): Oxidising power of halogens decreases in the order $F_2 > Cl_2 > Br_2 > I_2$, which is the basis of "Layer test". Statement (II): "Layer test" to identify $Br_2$ and $I_2$ in aqueous solution involves the oxidation of bromide or iodide into $Br_2$ or $I_2$ respectively with $Cl_2$, which is a type of displacement redox reaction. In the light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Question 10 · difficulty L2 · understanding

The oxidation state of chromium in the final product formed in the reaction between KI and acidified $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ solution is :

• A. +2
• B. +3
• C. +4
• D. +6