Which of the following statements associated with batteries are incorrect?
(A) Secondary batteries are rechargeable
(B) The cell potential of Leclanche cell is 1.5 V
(C) The cell reaction in a primary battery is reversible
(D) The efficiency of fuel cell is about 40%
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (C) and (D) only
A battery is one or more galvanic cells used as a source of electrical energy. Batteries are of two types:
Primary batteries: the reaction occurs only once; the battery becomes dead and cannot be recharged (dry cell, mercury cell).
Secondary batteries: the reaction can be reversed by passing current in the opposite direction, so they can be recharged (lead storage battery, nickel–cadmium cell).
Fuel cells convert the energy of combustion of fuels such as hydrogen directly into electricity and are much more efficient than thermal power plants.
Judging each statement:
(A) Secondary batteries are rechargeable — Correct. Their cell reaction is reversed on charging.
(B) The cell potential of Leclanche cell is 1.5 V — Correct. The Leclanché (dry) cell, with a zinc anode and a carbon rod in \( \ce{MnO2} \), gives about 1.5 V:
Anode: Zn(s) → Zn2+ + 2e−
Cathode: MnO2 + NH4+ + e− → MnO(OH) + NH3(C) The cell reaction in a primary battery is reversible — Incorrect. In a primary battery the reaction occurs only once and cannot be reversed.
(D) The efficiency of fuel cell is about 40% — Incorrect. A fuel cell has an efficiency of about 70%. About 40% is the efficiency of thermal power plants.
NCERT (2026-27 edition):
Secondary Batteries – “A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again. …”
Fuel Cells – “… The cell runs continuously as long as the reactants are supplied. Fuel cells produce electricity with an efficiency of about 70 % compared to thermal plants whose efficiency is about 40%. …”