Sodium and potassium ions move in and out of the axon when the membrane is

sodium and potassium ions move in and out of the axone when membrane is depolarized.

Explanation:

The sodium and potassium ions transfer in and out the axon through electrical process. This process is called depolarization and re-polarization.

Depolarization:

Depolarization is occur when stimulus is given to the resting neuron. In this process gates of sodium ions on the membrane become open and sodium ions that are present out side. inter into the cell. because of this process the charge of the nerve changes (-70 mv to -55 mV).

Re-polarization:

when the re-polarization occur, potassium gates are open and the potassium ions goes outside the membrane. During this process electrical potential becomes negative inside the cell until the potential of -70 mV is re-attain i.e, resting potential.

In short we can say that depolarization allow sodium ions to inter into the nerve membrane and re-polarization allow potassium ions to moves out side the membrane.

pure substance: iron,copper

impure substance: water,charcoal

your answer would be a. 12.5 kg