A population of birds lives on a small island. Another population of the same species lives on the mainland. The distance between the island and the mainland is too great for birds to fly back and forth. Recently, a series of sandbars and tiny islands have formed between the island and the mainland. What is the most likely effect of this?

An increase in gene flow between the bird populations.

Explanation:

The population of bird species living in the island and other one in mainland are geographically isolated because of the distance between the island and the mainland is large that does not allow birds to fly and cover the entire distance. This is the reason of reproductive isolation and restricts the gene flow between the two populations. But the creation of sandbars and tiny islands between the island and mainland created a way so that island and mainland birds can meet and reproduce. This will allow the increase in the gene flow between the two separated population of bird species.    

d. groundwater flows through the subsoil and deposits minerals.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added