Redox Reactions Test

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Redox Reactions Test - 65

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Weekly Quiz Competition

Question 1
1 / -0

The oxidation number of chlorine in HOCl is:

A
$$-1$$

B
$$zero$$

C
$$+1$$

D
$$+2$$

Solution

Let the oxidation number of $$Cl$$ in $${ HOCl }$$ be $$x$$. The oxidation states of $$H$$ and $$O$$ are $$+1$$ and $$-2$$ respectively. Since the atom as whole is neutral, following equation holds true:
$$1\times (+1)\quad +\quad 1\times (-2)\quad +\quad 1\times (x)\quad \quad =\quad 0\\ \Longrightarrow \quad 1\quad -\quad 2\quad +\quad x\quad =\quad 0\\ \Longrightarrow \quad x\quad =\quad 2-1\\ \Longrightarrow \quad x\quad =\quad 1$$

Hence, an answer is $$C$$.
Question 2
1 / -0

The oxidation state of Cr in $$K_2Cr_2O_7$$ is:

A
$$+7$$

B
$$+6$$

C
$$+3$$

D
$$+2$$

Solution

Let the oxidation number of $$Cr$$ in $${ K }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 }$$ be $$x$$. The oxidation states of $$K$$ and $$O$$ are +1 and -2 respectively. Since the atom as whole is neutral, following equation holds true:
$$2\times (+1)\quad +\quad 2\times (x)\quad +\quad 7\times (-2)\quad =\quad 0\\ \Longrightarrow \quad 2\quad +\quad 2x\quad -14\quad =\quad 0\\ \Longrightarrow \quad 2x\quad =\quad 14-2\\ \Longrightarrow \quad 2x\quad =\quad 12\\ \Longrightarrow \quad x\quad =\quad \dfrac { 12 }{ 2 } \quad =\quad 6$$

Hence, answer is $$B$$.
Question 3
1 / -0

The oxidation number of nitrogen in $$NO^-_3$$ is?

A
$$-1$$

B
$$+2$$

C
$$+3$$

D
$$+5$$

Solution

Let the oxidation number of $$N$$ in $${ { NO }_{ 3 } }^{ - }$$ be x. The oxidation state of oxygen is -2. Since the atom as whole is single negatively charged, following equation holds true:
$${ x\quad +\quad 3\quad \times \quad (-2)\quad =\quad -1 }\\ \Longrightarrow \quad x\quad -6\quad =\quad -1\\ \Longrightarrow \quad x\quad =\quad +6-1\\ \Longrightarrow \quad x\quad =\quad 5$$

Hence, answer is D.
Question 4
1 / -0

The oxidation number of arsenic atom in $$H_3AsO_4$$ is:

A
$$-1$$

B
$$-3$$

C
$$+3$$

D
$$+5$$

Solution

Let the oxidation number of $$As$$ in $${ H }_{ 3 }As{ O }_{ 4 }$$ be $$x$$. The oxidation states of $$H$$ and $$O$$ are $$+1$$ and $$-2$$ respectively. Since the atom as whole is neutral, following equation holds true:
$$3\times (+1)\quad +\quad 1\times (x)\quad +\quad 4\times (-2)\quad =\quad 0\\ \Longrightarrow \quad 3\quad +\quad x\quad -8\quad =\quad 0\\ \Longrightarrow \quad x\quad =\quad 8-3\\ \Longrightarrow \quad x\quad =\quad 5$$

Hence, answer is D.
Question 5
1 / -0

The oxidation state of chromium in chromium trioxide is?

A
$$+3$$

B
$$+4$$

C
$$+5$$

D
$$+6$$

Solution

Let the oxidation state of Chromium be $$x$$. Oxidation state of oxygen is -2
Therefore, $$1\times (x)+3\times (-2)=0\\ \Longrightarrow x-6=0\\ \Longrightarrow x=+6$$
Hence, Option D is the correct answer.
Question 6
1 / -0

Among the following, identify the species with an atom in $$+6$$ oxidation state.

A
$$MnO^-_4$$

B
$$Cr(CN)^{3-}_6$$

C
$$NiF^{2-}_6$$

D
$$CrO_2Cl_2$$
Solution
Hint:

The total number of electrons an atom can lose or gain to form a bond with other elements is called the oxidation state of that atom.

Explanation:
- In $$ MnO_{4}^{-}$$, let the oxidation state of $$Mn$$ be $$x$$
$$ x\ +\ (4\left ( -2 \right ))=-1$$ $$ \Rightarrow x=+7$$.
- In $$ Cr\left ( CN \right )_{6}^{3-}$$, let the oxidation state of $$Cr$$ be $$y$$
$$ y\ +\ (6\left ( -1 \right ))=-3$$ $$ \Rightarrow y=+3$$.
- In $$ NiF_{6}^{2-}$$, let the oxidation state of $$Ni$$ be $$z$$
$$ z\ +\ (6\left ( -1 \right ))=-2$$ $$ \Rightarrow z=+4$$.
- In $$ CrO_2Cl_2$$, let the oxidation state of $$Cr$$ be $$q$$
$$ q\ +\ (2\left ( -2 \right ))\ +\ (2\left ( -1 \right ))=0$$ $$ \Rightarrow q=+6$$.

Hence, $$ CrO_2Cl_2$$ has $$+6$$ oxidation state.

Therefore, the correct answer is option $$D.$$
Question 7
1 / -0

The oxidation state of iodine in $$H_4IO^-_6$$ is?

A
$$+7$$

B
$$-1$$

C
$$+5$$

D
$$+1$$

Solution

Let the oxidation number of I in $${ H }_{ 4 }I{ { O }_{ 6 } }^{ - }$$ be x. The oxidation states of $$H$$ and $$O$$ are +1 and -2 respectively. Since the atom as whole is single negatively charged, following equation holds true:

$$4\times (+1)\quad +\quad 1\times (x)\quad +\quad 6\times (-2)\quad =\quad -1\\ \Longrightarrow \quad 4\quad +\quad x\quad -\quad 12\quad =\quad -1\\ \Longrightarrow \quad x\quad =\quad 12-4-1\\ \Longrightarrow \quad x\quad =\quad +7$$

Hence, answer is A.
Question 8
1 / -0

Oxidation number of N in $$NH_4NO_3$$ is:

A
$$-3$$

B
$$+5$$

C
$$-3$$ and $$+5$$

D
$$+3$$ and $$-5$$

Solution

$$NH_4NO_3$$ exists as $$NH_4^{+}$$ and $$NO_3^{-}$$.Oxidation state of $$N$$ in $$NH_4^{+}$$ is -3 and in $$NO_3^{-}$$ is +5.
Note: Oxidation state of oxygen is -2 and of hydrogen is +1.
Question 9
1 / -0

Oxidation number of xenon in $$XeOF_2$$ is___________.

A
Zero

B
$$2$$

C
$$4$$

D
$$3$$

Solution

$${ XeO{ F }_{ 2 } }$$ can be written as $$XeO{ F }_{ 2 }$$ Let the oxidation number of $$Xe$$ in $${ XeO{ F }_{ 2 } }$$ be x. The oxidation states of $$O $$ and $$F$$ are +2 and -1 respectively
(The oxidation state of $$O$$ in $$O{ F }_{ 2 }$$ is +2 (exception case) as fluorine is most electronegative element with oxidation state of -1 (to keep the atoms neutral here). Since the atom as whole is neutral, following equation holds true:

$$1\times (x)\quad +\quad 1\times (+2)\quad +\quad 2\times (-1)\quad =\quad 0\\ \Longrightarrow \quad x\quad +\quad 2\quad -\quad 2\quad =\quad 0\\ \Longrightarrow \quad x\quad =\quad 0$$

Hence, answer is A.
Question 10
1 / -0

Match the List - I with List - II and select the correct matching from the codes given below:
Column - I Column - II
A. $$NaN_3$$ 1. +5
B. $$N_2H_4$$ 2. +1
C. $$NH_2OH$$ 3. -1/3
D. $$N_2O_5$$ 4. -2

A
A-3 B-4 C-2 D-1

B
A-4 B-3 C-1 D-2

C
A-3 B-4 C-1 D-2

D
A-4 B-3 C-2 D-1

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Column - I	Column - II
A. $$NaN_3$$	1. +5
B. $$N_2H_4$$	2. +1
C. $$NH_2OH$$	3. -1/3
D. $$N_2O_5$$	4. -2

Redox Reactions Test - 65

Result

Redox Reactions Test - 65

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Question 1

$$-1$$

$$zero$$

$$+1$$

$$+2$$

Solution

Question 2

$$+7$$

$$+6$$

$$+3$$

$$+2$$

Solution

Question 3

$$-1$$

$$+2$$

$$+3$$

$$+5$$

Solution

Question 4

$$-1$$

$$-3$$

$$+3$$

$$+5$$

Solution

Question 5

$$+3$$

$$+4$$

$$+5$$

$$+6$$

Solution

Question 6

$$MnO^-_4$$

$$Cr(CN)^{3-}_6$$

$$NiF^{2-}_6$$

$$CrO_2Cl_2$$

Solution

Question 7

$$+7$$

$$-1$$

$$+5$$

$$+1$$

Solution

Question 8

$$-3$$

$$+5$$

$$-3$$ and $$+5$$

$$+3$$ and $$-5$$

Solution

Question 9

Zero

$$2$$

$$4$$

$$3$$

Solution

Question 10

A-3 B-4 C-2 D-1

A-4 B-3 C-1 D-2

A-3 B-4 C-1 D-2

A-4 B-3 C-2 D-1

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