Answer: C) 0.020 m
Explanation:
Molality of a solution is defined as the number of moles of solute dissolved per kg of the solvent.

where,
n = moles of solute
= weight of solvent in g
Mole fraction of
is =
i.e.
moles of
is present in 1 mole of solution.
Moles of solute
= 
moles of solvent (water) = 1 -
= 0.99
weight of solvent =
Molality =
Thus approximate molality of
in this solution is 0.020 m
D=mxv so your answer should be 269.37
O is what should go in the blank. O stands for Oxygen.
The geosphere is about 99.94% of Earth's mass, so C is the answer.