As a substance changes from a liquid to a gas, the average distance between molecules..

( 1 ) decreases
( 2) increases
( 3) remains the same

increases

Explanation:

Matter exists in three different states, they are solids, liquids and gases. And each of them contains molecules with a certain amount of kinetic energy.

Hence, the addition of heat changes a substance from a liquid to a gas through a process called vaporization, whereby liquid molecules on changing to gases acquire a higher kinetic energy, and move more freely within the containing vessel.

Thus, the higher kinetic energy explains the increase in the average distance between molecules.

percent abundance for cu-63 can be shown as:

63 x + 65 (1-x) = 62.9296

65 - 62.9296 = 2 x

x = 1.035

thus, percent abundance for cu-63 is 1.035

percent abundance for cu-65 can be shown as:

63 x + 65 (1-x) = 64.9278

65 - 64.9278 = 2 x

x = 0.0361

thus, percent abundance for cu-63 is 0.0361

the mass spectrum of cu-63 showing the intense peak as, this isotope is found in nature more abundantly around 92.38 % in comparison to cu-65 which is found 62.58 % naturally