Answer:
Density is the correct answer choice.
Answer:different elements have different number of electrons and shells/orbits thatswhy it have different atomic mass and size.
Explanation:

Actually Welcome to the concept of Bond Formation.
Answer is :-
B.) O and Cl
These both are Non-Metals with high Electronegativity nature, hence none of them can share electrons to foram any bond to eventually form a Electro valentines Compound.
Answer
A *single covalent bond* is formed by sharing one pair of valence electrons.They are less reactive comparatviely and have a high bond length
A *double covalent bond* is formed by sharing two pairs of valence electrons.They are moderately reactive and have moderate bond length.
A *triple covalent bond* is formed by sharing three pairs of valence electrons.They are highly reactive and have a low bond length.