Density = mass / volume so
Density = 156 / 20.0
Density = 7.8 g/mL
It's formed by the hydrogen ion of the acid and the hydroxide of the base.

Sulfuric Acid + potassium superoxide --> Potassium Sulfate + Heavy Water
Hope this Helps :)
3 first sig fig
6 second sig fig
5 third sig fig
4 not more than 5, so do not change 5 to 6
0.0365
Atoms of the same element but with different atomic masses are called isotopes. They possess a different atomic mass, due to the indifferent number of neutrons that the atoms of a given element have.