The correct answer is option 4 - Lithium. Lithium is prominently used in mobile phone batteries.
Option 1 - Copper is commonly used in electrical wiring and transmission of electricity, but it is not prominently used in mobile phone batteries.
Option 2 - Zinc is commonly used in galvanizing and as a protective coating for metals, but it is not prominently used in mobile phone batteries.
Option 3 - Nickel is often used in rechargeable batteries, but it is not prominently used in mobile phone batteries.
Lithium, on the other hand, is the main component of the battery in a mobile phone. Lithium-ion batteries are known for their high energy density, which allows them to provide a long-lasting charge. These batteries can also be recharged multiple times, making them ideal for use in mobile devices. The use of lithium in mobile phone batteries has become widespread due to its lightweight nature and ability to store and release energy efficiently.
Therefore, the correct answer is option 4 - Lithium.