In plotting of cost functions, level of activities according to which charged cost is represented on

The correct answer is A. x-axis.

The x-axis is the horizontal axis on a graph, and it represents the independent variable. In the case of a cost function, the independent variable is the level of activity. The y-axis is the vertical axis on a graph, and it represents the dependent variable. In the case of a cost function, the dependent variable is the cost.

Option B is incorrect because the y-axis represents the cost. Option C is incorrect because the unit axis is not a standard axis on a graph. Option D is incorrect because the term axis is not a standard axis on a graph.