Redox Reactions Chapter-Wise Test 3

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the oxidation number of chlorine in \( \ce{KClO3} \)?

Let Cl = \( x \). K = +1, O = -2. Equation: \( +1 + x + 3(-2) = 0 \), \( 1 + x - 6 = 0 \), \( x = +5 \).

+1
+3
+5
+7
3

Which reaction is an example of a combination redox reaction?

In \( \ce{S + O2 -> SO2} \), S (0 to +4) is oxidized, and O₂ (0 to -2) is reduced, combining into one product.

\( \ce{CaO + H2O -> Ca(OH)2} \)
\( \ce{S + O2 -> SO2} \)
\( \ce{2NaCl -> 2Na + Cl2} \)
\( \ce{NaOH + HCl -> NaCl + H2O} \)
2

What is the oxidation number of oxygen in \( \ce{H2O2} \)?

In peroxides, O has an oxidation number of -1. For \( \ce{H2O2} \): \( 2(+1) + 2x = 0 \), \( 2x = -2 \), \( x = -1 \).

-2
-1
+1
+2
2

What is the oxidation number of chlorine in \( \ce{ClO2} \)?

Let Cl = \( x \). O = -2. Equation: \( x + 2(-2) = 0 \), \( x - 4 = 0 \), \( x = +4 \).

+2
+3
+1
+4
4

What is the oxidation number of phosphorus in \( \ce{P4} \)?

In its elemental form, \( \ce{P4} \), phosphorus has an oxidation number of 0.

+3
+5
-3
0
4

In \( \ce{2KMnO4 + 16HCl -> 2MnCl2 + 5Cl2 + 2KCl + 8H2O} \), which species contains the element reduced?

Mn (+7 in \( \ce{KMnO4} \)) becomes +2 in \( \ce{MnCl2} \), gaining electrons; it’s the reduced species.

\( \ce{HCl} \)
\( \ce{Cl2} \)
\( \ce{MnCl2} \)
\( \ce{KMnO4} \)
3

In \( \ce{2Cr(OH)3 + 3H2O2 + 4NaOH -> 2Na2CrO4 + 8H2O} \), how many electrons are lost per chromium atom?

Cr (+3 in \( \ce{Cr(OH)3} \)) to +6 in \( \ce{CrO4^2-} \): change = +6 - (+3) = +3; each Cr loses 3 electrons.

3
2
4
1
1

In the reaction \( \ce{2AgNO3 + H2S -> Ag2S + 2HNO3} \), which species is oxidized?

Oxidation involves electron loss. S (-2 in \( \ce{H2S} \)) becomes -2 in \( \ce{Ag2S} \), but Ag (+1 to 0) is reduced; S is oxidized contextually.

\( \ce{H2S} \)
\( \ce{AgNO3} \)
\( \ce{Ag2S} \)
\( \ce{HNO3} \)
1

What is the oxidation number of bromine in \( \ce{BrF3} \)?

Let Br = \( x \). F = -1. Equation: \( x + 3(-1) = 0 \), \( x - 3 = 0 \), \( x = +3 \).

+1
+5
+7
+3
4

In \( \ce{PbS + 4H2O2 -> PbSO4 + 4H2O} \), which species is the reducing agent?

\( \ce{PbS} \) (S: -2 to +6 in \( \ce{PbSO4} \)) loses electrons, reducing \( \ce{H2O2} \) (O: -1 to -2).

\( \ce{H2O2} \)
\( \ce{PbS} \)
\( \ce{PbSO4} \)
\( \ce{H2O} \)
2

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