# Chemistry Class 11 NCERT Solutions Chapter 8 Redox Reactions Part 3

Q: 3. Justify that the following reactions are redox reactions:

(A)

(B)

(C)

(D)

(E)

Answer:

(A)

Let us write the oxidation number of each element involved in the given reaction as:

Here, the oxidation number of Cu decreases from +2 in to 0 in Cu i.e., CuO is

reduced to . Also, the oxidation number of H increases from 0 in to +1 in i.e.,

is oxidized to . Hence, this reaction is a redox reaction.

(B)

Here, the oxidation number of Fe decreases from +3 in to 0 in Fe i.e., is reduced to Fe. On the other hand, the oxidation number of C increases from +2 in CO to +4 in i.e., CO is oxidized to . Hence, the given reaction is a redox reaction.

(C)

The oxidation number of each element in the given reaction can be represented as:

In this reaction, the oxidation number of B decreases from +3 in to –3 in . i.e.,

is reduced to . Also, the oxidation number of H increases from –1 in to

+1 in i.e., is oxidized to . Hence, the given reaction is a redox reaction.

(D)

The oxidation number of each element in the given reaction can be represented as

In this reaction, the oxidation number of K increases from 0 in K to +1 in KF i.e., K is oxidized to KF. On the other hand, the oxidation number of F decreases from 0 in to -1 in KF i.e, is reduced to KF.

Hence, the above reaction is a redox reaction.

(E)

The oxidation number of each element in the given reaction can be represented as

Here, the oxidation number of N increases from –3 in NH3 to +2 in NO. On the other hand, the oxidation number of decreases from 0 in to –2 in NO and i.e., is reduced. Hence, the given reaction is a redox reaction.

Q: 4. Fluorine reacts with ice and results in the change

Justify that this reaction is a redox reaction.

Answer:

Let us write the oxidation number of each atom involved in the given reaction above its symbol as:

Here, we have observed that the oxidation number of F increases from 0 in to +1 in . Also, the oxidation number decreases from 0 in to –1 in . Thus, in the above reaction, F is both oxidized and reduced. Hence, the given reaction is a redox reaction.

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