Elements in the same group have D. Same number of valence electrons.
You should read up on Proust's law, better known as the Law of Definite Proportions. This is a chemical law that defines your question more generally, on why the ratio of elements and ions are always fixed.
Basically, this compound Magnesium(II) Chloride is MgCl2 because it has the same number of protons, neutrons, and electrons all the way. This defines the properties of the compound or atom.
the unnamed spacecraft which travels to Mars, will have the greatest weight on the Earth.
a is the answer because all of the other answers are wrtong
Homogeneous or heterogeneous, Hope this helps!!