Which of the following statements are true for primary batteries?
A. Primary battery can be recharged again once they are dead.
B. Mercury cell is an example of primary battery.
C. A paste of KOH and ZnO is used as an electrolyte in mercury cell.
D. The anode in mercury cell consists of zinc-mercury amalgam.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B, C and D only
A primary battery works only once and cannot be recharged; a secondary battery (e.g. the lead storage battery) is recharged by passing current through it in the opposite direction.
A. Primary battery can be recharged again once they are dead. — Incorrect. A primary battery cannot be recharged; the ability to be recharged is what defines a secondary battery.
B. Mercury cell is an example of primary battery. — Correct. The mercury cell is used once and discarded; it is not recharged.
C. A paste of KOH and ZnO is used as an electrolyte in mercury cell. — Correct. The KOH-ZnO paste supplies the \( \ce{OH^{-}} \) ions used at the anode and formed at the cathode.
D. The anode in mercury cell consists of zinc-mercury amalgam. — Correct. Zinc amalgam, Zn(Hg), is the anode; the cathode is a paste of HgO and carbon.
NCERT (2026-27 edition):
Primary Batteries
