A physical change occur when objects or substances undergo a change that does not change in which the composition of a substance changes or one or more substances combine or break up from new substances.
A population that has been isolated, especially a smaller one, could have a high level of homozygosity and therefore not a lot of genetic variation. Gene flow between such populations can increase the level of heterozygosity, and therefore up genetic variation.
Answer:
Dry air is a mechanical mixture of nitrogen, oxygen, argon and several other gases in minor amounts.
Explanation: