4 m/s^2
I hope this helps!
The correct option is C.
The density of an object refers to its mass per volume. Water and ice have different densities. The differences in their densities is due to the empty spaces which exist in the structure of ice. Because of the empty spaces, the structure of ice occupy more volume than that of water, hence it is less dense than water.
I have provided the steps and solution within the attachment. The pH of the solution would be 12.30, this indicates that the solution is basic, as a higher value of pH indicates presence of more hydroxide ions and less of hydrogen ions in the solution.