Explain how to identify a starting position on a line

We can easily find out the beginning point of the line by using dot representation. When it comes to position vector, it expresses the exact position of certain object from the starting point of the coordinate system. The vector is a straight line that has a certain end which is fixed to its body.

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

The answer is d.potassium