The correct answer is option 4, Sodium.

Sodium is an essential mineral that plays a crucial role in the transmission of nerve impulses in the nerve fibers of the human body. Nerve impulses are electrical signals that travel along nerve fibers to transmit information throughout the body.

Sodium is responsible for maintaining the electrical potential across the cell membrane of nerve cells, which allows the nerve impulses to travel effectively. It achieves this by regulating the flow of ions across the membrane through specialized channels called ion channels.

When a nerve impulse is generated, sodium ions rapidly move into the cell, creating a positive charge inside the cell. This change in electrical potential triggers the propagation of the nerve impulse along the nerve fiber.

Other minerals, such as calcium, cobalt, and iodine, are important for various physiological functions in the human body but are not directly involved in the transmission of nerve impulses.

Therefore, Sodium is the essential mineral for the transmission of nerve impulses in the nerve fibers of the human body.