Final answer:
The family leaving California for Idaho would lead to emigration, resulting in a decrease in option (d) in California's population. Emigration is when individuals move out of a population.
Step-by-step explanation:
After a family left California to live in Idaho, the population change in California would be categorized as emigration. Emigration refers to the movement of individuals out of a population, which in this case is the state of California. Consequently, emigration would lead to a population decrease in California.
Emigration, along with immigration, births, and deaths, are all factors that determine population growth according to the population growth equation. In this scenario, since the family moved out of California, it would not fall under immigration.
Immigration is when people move into an area to take up permanent residence, whereas emigration is when people move out.