To solve this problem it is necessary to apply the concepts related to the Kinetic Energy and the Energy Produced by the heat loss. In mathematical terms kinetic energy can be described as:

Where,
m = Mass
v = Velocity
Replacing we have that the Total Kinetic Energy is



On the other hand the required Energy to heat up t melting point is


Where,
m = Mass
Specific Heat
Change at temperature
Latent heat of fussion
Heat required to heat up to melting point,




The energy required to melt is larger than the kinetic energy. Therefore the heat of fusion of lead would be 327 ° C: The melting point of lead.
Explanation:
We need to calculate the speed of light in each materials
(I). Gallium phosphide,
The index of refraction of Gallium phosphide is 3.50
Using formula of speed of light
....(I)
Where,
= index of refraction
c = speed of light
Put the value into the formula


(II) Carbon disulfide,
The index of refraction of Gallium phosphide is 1.63
Put the value in the equation (I)


(III). Benzene,
The index of refraction of Gallium phosphide is 1.50
Put the value in the equation (I)


Hence, This is the required solution.