A straight line drawn through the centre and touching the circumference on each side is called the:

The diameter is defined as a straight line that passes through the center of a circle and touches the circumference at two points on opposite sides. This means it is the longest chord of the circle and effectively divides the circle into two equal halves. Because it goes through the center, the diameter is always twice the length of the radius, which is the line segment from the center of the circle to any point on the circumference.

In contrast, the radius refers to the distance from the center to the edge of the circle and is not a straight line that intersects the circumference at two points. The circumference is the outer boundary of the circle itself, rather than a defining line within it. A chord is any line segment with both endpoints on the circle, but it does not have to pass through the center, which differentiates it from the diameter. Thus, the definition of the diameter aligns perfectly with the characteristics of the line drawn through the center and touching the circumference on both sides.