Which of the following reactions could be used to power a battery because of the transfer of electrons? pb22+ + 2br− → pbbr cacl2 + 2naoh → ca(oh)2 + 2nacl koh + hcl → kcl + h2o zn + cu2+ → zn2+ + cu

Answer is: Zn + Cu2+ → Zn2+ + Cu.

In this chemical reaction, there is transfer of electrons from zinc (Zn) to copper (Cu). Zinc change oxidation number from 0 to +2 (lost electrons) and copper change oxidation number from +2 to 0 (gain electrons).

Oxidation half reaction: Zn⁰ → Zn²⁺ + 2e⁻.

Reduction half reaction: Cu²⁺ + 2e⁻ → Cu⁰.

In other chemical reactions, there is no change of oxidation number of elements.

while cooking a piece of 1/2 pound beef steak, a cast iron pan (2.4kg in weight) was heated 260 celsius.