In the electrochemical series written in the increasing order of reduction potential
(A) The elements which are placed above the hydrogen in the electrochemical series are stronger oxidizing agents.
(B) The elements which are placed above the hydrogen in the electrochemical series are stronger reducing agents.
(C) The elements with the positive electrode potential values lie below the hydrogen in the electrochemical series.
(D) The activity of both the metals and non-metals in the electrochemical series decreases from top to bottom.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B) and (C) only
In the electrochemical series written in increasing order of standard reduction potential, the species with the most negative \( E^{\circ} \) (Li, K) are at the top, hydrogen (\( E^{\circ} = 0 \)) is in between, and the species with the most positive \( E^{\circ} \) (\( \ce{F2} \)) are at the bottom. A low reduction potential means the element gives up electrons easily and is a strong reducing agent; a high reduction potential means the species takes up electrons easily and is a strong oxidising agent.
(A) The elements which are placed above the hydrogen in the electrochemical series are stronger oxidizing agents. — Incorrect. Elements above hydrogen have negative \( E^{\circ} \); they lose electrons readily, so they are reducing agents, not oxidising agents.
(B) The elements which are placed above the hydrogen in the electrochemical series are stronger reducing agents. — Correct. With negative \( E^{\circ} \) they are oxidised more easily than hydrogen; for example, zinc displaces hydrogen from acids:
\( \displaystyle \ce{Zn(s) + 2H+(aq) -> Zn^2+(aq) + H2(g)} \)
(C) The elements with the positive electrode potential values lie below the hydrogen in the electrochemical series. — Correct. Hydrogen is taken as zero, and the series is arranged in increasing \( E^{\circ} \), so every positive value (Cu +0.34 V, Ag +0.80 V) comes after it.
(D) The activity of both the metals and non-metals in the electrochemical series decreases from top to bottom. — Incorrect. The activity of the metals (their reducing power) decreases from top to bottom, but the activity of the non-metals (their oxidising power) increases from top to bottom: \( \ce{F2} \), at the bottom, is the most reactive non-metal. The statement does not hold for both.
Note: NTA accepted both Option (1) and Option (4) in the Final Answer Key. Option (4) originally read “(B), (C) and (D) only”; it was also accepted because statement (D) is true for the metals of the series, whose activity decreases from top to bottom. So that students are not confused and only one option is correct, Option (4) has been changed to “(A), (C) and (D) only”.