Their weights could be different.
Their volumes could be different.
Their densities could be different.
The volume for an ounce of lead is much different than an ounce of aluminum.
the weight of a cubic meter of balsa wood is much different (and much lighter) than a cubic meter of water. That's why the ancients used balsa for their rafts.
B because....................
Answer:
It will have 5 valence electrons as its in group 5.
The atom will gain as its closer to the full configuration 8.
The charge will be 3- as it will gain 3 electrons.
The compound formed by chlorine and barium is 
as the number of valence electrons in barium is 2 and in chlorine is 1. In this compound, barium acts as a cation and chlorine acts as an anion. The formation of the compound is as shown in the image.
Since, barium is an element of Group-2 (alkaline earth metal) so the other element that has a chemical formula most and least similar to the chemical formula of the compound formed by chlorine and barium should be from Group-2 (alkaline earth metal) only which has properties somewhat like barium. So, the element is strontium.
Strontium forms a compound with formula 
in which strontium acts as a cation and chlorine acts as an anion. The formation of the compound is as shown in the image.
