Hm, this could be more than one option, but gaining electrons makes a negative charge, so
If atoms of a halogen nonmetal (Group 17) gains one electron, the atoms the have "a negative one charge".
It's B. Since density equals mass/volume. The missing quantity needed is mass.Hope this helps.
Answer: 4.90
Explanation: The molal freezing point constant of C6H6 is 4.90 and its melting point is 5.51∘C. A solution of 0.816 g of a compound A dissolved in 7.5 g of benzene freezes at 1.59∘C. Calculate molecular weight of compound A