Consider the following statements regarding a motor car battery : I. The voltage is usually 12 V. II. Electrolyte used is hydrochloric acid. III. Electrodes are lead and copper. IV. Capacity is expressed in ampere-hour. Which of the above statements are correct ?

The correct choice is option 4 (I and IV). Motor-car batteries are nominally 12 V units commonly used in automobiles. The electrolyte in such lead–acid batteries is a dilute solution of sulfuric acid (H2SO4), not hydrochloric acid; the active plates are lead (Pb) and lead dioxide (PbO2) which participate in the charge–discharge reactions. Battery capacity is normally expressed in ampere-hours (Ah), representing the charge delivered over time, so statement IV is correct. Therefore statements I and IV are correct while II and III are incorrect.