Which diagram shows a voltaic cell?

Since you have not included the figures with the diagrams to select the right answer, I am going to explain the main differences that lead you to differentiate electrochemical cells.

There are four important terms needed to identify the electrochemical cells: electrolysis, electrochemical cells, electrolitc cells and voltaic cells.

1) Electrochemical cell: is a device that uses a chemical reaction (redox reaction) to produce electricity or that uses electricity to product a chemical reaction.

2) Electrolysis: is the production of a chemical reaction using electricity.

3) Electroltic cell: is one of the two types of electrochemical cell. It is that in which electricity is used to produce the chemical reaction, i. e. where electrolysis happens. For example, the decomposition of sodium chloride brines is done in an electrolitic cell.

4) Galvanic cell: is the other type of electrochemical cell. It is that in which chemical reactions (redox reactions) produce electricity. The battery of the car is an example of a galvanic cell.

Here you are asked to identify which diagram shows a voltaic cell. So, you need to lool at:

- a redox reaction is happening

- this redox reaction is producing electricity (not that the electricity is producing the reaction)

Remember that a redox reaction is where some atoms are being reduced (gaining electros) and others are being oxidized (losing electrons).

Tha information will let you to choose the righ diagram.