Asubstance changes from a solid to a liquid at its a. lowest density b. highest density c. boiling point d. melting point

Option (D) is the correct answer.

Explanation:

When we heat a solid substance then at a certain temperature point it starts to convert or melt into liquid state. This point of change is known as melting point.

For example, when ice melts at room temperature then it means ice is melting at 25 degree celsius.

When liquid state of a substance changes into vapor state upon heating. Then the point at which this change occurs is known as boiling point.

Also, more is the mass of a solid substance per unit volume highest will be its density. And, less is the mass of a solid substance per unit volume lowest will be its density.

Thus, we can conclude that a substance changes from a solid to a liquid at its melting point.

half of a circle

explanation:

the arrow and the top of the circle is matching together. it is not a polygon because a polygon would always be the same shape. therefore, an half of a circle is called semicircle so you would find the radius of it.