The best answer would be C.
The mass of an element depends on the number of particles found in the nucleus of the atom. Atomic mass can be computed by adding the number of protons and the number of neutrons. Protons and neutrons are found in the nucleus of an atom. So the answer must be letter C.
You are correct it is translucent because opaque let’s no light through but transparent lets almost all light through
The answer is 12.36. hoped this helped!