2. What is the percentage by mass of sodium (Na) in a formula unit of sodium
hydrogen carbonate (NaHCO3)?

27.367%

Explanation:

In the example, the solution mass is equal to mass (NaCl) + mass (NaHCO3) + mass (water) = 10 g + 6 g + 120 g = 136 g. Divide the mass of the first dissolved component by the solution mass, and then multiply the result by 100 to calculate the mass percentage.

-sciencing.com

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.