A change of state (which is a physical change) can cause gas.
The arrangement of molecules within the 3 phases of matter are shown in the picture.
For the solid, the molecules are packed closely together. They don't have much space to move, so they just practically vibrate. For the liquid, the molecules are relatively farther from each other. The liquid molecules can flow freely but not as much as the gases. In the gases, the molecules are very far from each other. They are very sensitive to slight changes of pressure, volume and temperature.
Due to hydrogen bonding there is a formation of cage like structure called lattice in ice due to which <span> density of ice is less than that of water. Moreover, it is a known fact that density of water is maximum at 4°C.</span>
To calculate the average mass of the element, we take the summation of the product of the isotope and the percent abundance. We calculate as follows:
Average atomic mass = .374 ( 184.953 amu ) + .626 ( <span>186.958 amu ) = 186.208 amu
Hope this answers the question. Have a nice day.</span>