Given below are reduction potentials:

(A) \(E^o_{Cu^{2+}/Cu} = 0.34 V\)

(B) \(E^o_{Sn^{2+}/Sn} = -0.14 V\)

(C) \(E^o_{Zn^{2+}/Zn} = -0.76 V\)

(D) \(E^o_{K^+/K} = -2.93 V\)

The strongest reducing agent from the above is:

K

The correct answer is option 4. K.

The concept of standard reduction potential (\(E^o\)) is used to measure the tendency of a species to gain electrons and undergo reduction. The more negative the standard reduction potential, the stronger the reducing agent.

Given reduction potentials:

(A) \(E^o_{Cu^{2+}/Cu} = 0.34 \, \text{V}\)

(B) \(E^o_{Sn^{2+}/Sn} = -0.14 \, \text{V}\)

(C) \(E^o_{Zn^{2+}/Zn} = -0.76 \, \text{V}\)

(D) \(E^o_{K^+/K} = -2.93 \, \text{V}\)

The most negative standard reduction potential belongs to potassium (\(K^+/K\)), which is \(-2.93 \, \text{V}\). A more negative value indicates a stronger tendency to be reduced or act as a reducing agent.

Potassium (\(K\)) is the strongest reducing agent among the options provided.

Therefore, the correct answer is: 4. \(K\)