The melting point of a particular compound is fixed and it is an important identification of an unknown compound. The practice to determine the melting point of an unknown material In different ratio with a known material is important to get the exact melting point of the unknown material. In different ratio the melting point of the unknown material will be fixed as the melting point of a pure material doesn't depend on the ratio in which they are mixed with other material. To get the exact melting point it is always good to get the melting point twice in different ratio.
The answer to your question is D.
Endothermic is when the compound absorbs energy in the reaction. Exothermic is the opposite: the compound releases energy in the reaction.
Through J.J. Thomson's creative mind, he proposed the "Plum Pudding Theory" which shows the scientific model of an atom wherein electrons are attached to the body of the atom as if it was like a raisin in a pudding. He also consolidates the properties of atoms at that time such as: electrons are negatively charge particles and and atom has neutral charge.