What is the unit of electric potential difference?

When is the potential difference between two points said to be $1$ volt?

$(a)$ Define the term 'volt'.
$(b)$ State the relation between work,charge,and potential difference for an electric circuit. Calculate the potential difference between the two terminals of a battery,if $100 \ J$ of work is required to transfer $20 \ C$ of charge from one terminal of the battery to the other.

Which of the following formulas represents voltage $(V)$?

What is potential difference? Is it a scalar quantity or a vector quantity? Give its $SI$ units.

Is electrostatic potential a scalar quantity or a vector quantity?