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  4. Redox Reactions Chapter-Wise Test 19

Redox Reactions Chapter-Wise Test 19

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the oxidation number of phosphorus in \( \ce{H3PO4} \)?

Let P = \( x \). H = +1, O = -2. Equation: \( 3(+1) + x + 4(-2) = 0 \), \( 3 + x - 8 = 0 \), \( x = +5 \).

+3
+5
+1
-3
2

In \( \ce{2Na2S2O3 + I2 -> Na2S4O6 + 2NaI} \), which element undergoes oxidation?

S (+2 avg. in \( \ce{S2O3^2-} \)) becomes +2.5 avg. in \( \ce{S4O6^2-} \), losing electrons; I (0 to -1) is reduced.

Iodine
Sodium
Oxygen
Sulfur
4

In the reaction \( \ce{3CuO + 2NH3 -> 3Cu + N2 + 3H2O} \), how many electrons are gained per copper atom?

Cu (+2 in \( \ce{CuO} \)) to 0 in \( \ce{Cu} \): change = 0 - (+2) = -2, meaning 2 electrons gained per Cu atom.

1
2
3
4
2

In \( \ce{2H3PO3 -> H3PO4 + PH3} \), how many electrons are transferred per mole of \( \ce{H3PO3} \)?

P (+3 in \( \ce{H3PO3} \)) to +5 in \( \ce{H3PO4} \) and -3 in \( \ce{PH3} \). 1 P loses 2 e⁻, 1 P gains 6 e⁻; total = 4 e⁻ per 2 \( \ce{H3PO3} \), so 2 per mole.

1
3
4
2
4

Which of the following is a redox reaction involving a displacement process?

In \( \ce{2Al + 3NiSO4 -> Al2(SO4)3 + 3Ni} \), Al (0 to +3) is oxidized, and Ni (+2 to 0) is reduced, with Al displacing Ni.

\( \ce{2Al + 3NiSO4 -> Al2(SO4)3 + 3Ni} \)
\( \ce{NaCl + AgNO3 -> AgCl + NaNO3} \)
\( \ce{2NaOH + H2SO4 -> Na2SO4 + 2H2O} \)
\( \ce{CaCO3 -> CaO + CO2} \)
1

In \( \ce{2H2S + SO2 -> 3S + 2H2O} \), what is the total number of electrons transferred per mole of \( \ce{SO2} \)?

S (+4 in \( \ce{SO2} \)) to 0 in \( \ce{S} \): 1 S gains 4 electrons. 2\( \ce{H2S} \) (S: -2 to 0): 2 S lose 4 electrons total. Per \( \ce{SO2} \) = 4.

2
6
4
8
3

In the reaction \( \ce{2Ag2O -> 4Ag + O2} \), which species is reduced?

Reduction involves electron gain. Ag (+1 in \( \ce{Ag2O} \)) becomes 0 in \( \ce{Ag} \), gaining electrons.

\( \ce{O2} \)
\( \ce{Ag} \)
\( \ce{Ag2O} \)
None of these
2

In \( \ce{2CrO3 + 3H2O2 + 2KOH -> 2KCrO4 + 4H2O} \), how many electrons are transferred per mole of \( \ce{CrO3} \)?

Cr (+6 in \( \ce{CrO3} \)) remains +6 in \( \ce{CrO4^2-} \); O (-1 in \( \ce{H2O2} \)) to -2: 3 O gain 6 electrons total. No redox for Cr; focus on H₂O₂, but per \( \ce{CrO3} \) context = 0 for Cr change.

2
1
0
3
3

What is the oxidation number of sulfur in \( \ce{SO3} \)?

Let S = \( x \). O = -2. Equation: \( x + 3(-2) = 0 \), \( x - 6 = 0 \), \( x = +6 \).

+4
+2
+6
0
3

Which reaction is an example of a displacement redox reaction?

In \( \ce{2Al + 3NiSO4 -> Al2(SO4)3 + 3Ni} \), Al (0 to +3) is oxidized, and Ni (+2 to 0) is reduced, with Al displacing Ni.

\( \ce{2Na + 2H2O -> 2NaOH + H2} \)
\( \ce{2Al + 3NiSO4 -> Al2(SO4)3 + 3Ni} \)
\( \ce{2H2O2 -> 2H2O + O2} \)
\( \ce{CaCO3 -> CaO + CO2} \)
2

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