The hot water remains at the top of chilled water.
Explanation:
The hot water remains at the top of chilled water because hot water has less denser as compared to chilled water. Due to higher density of chilled water, it remains at the bottom due to its greater mass while on the other hand, the hot freshwater goes upward and spreads at the top of the chilled water due to lower mass so when the hot water is added to the chilled water, hot water remains at the top.
mass number remains constant while atomic number has been increased by 1 unit . beta is electron like element where its mass number is 0 and atomic number is -1.