Some blind cave salamander have eye how might this be evidence that cave salamander evolved from sighted ancestors

Eyes would be a vestigial structure.

Explanation:

A vestigial structure as a stunted organ that has little or no function in a particular organism. An example of this can be seen in the question above which states that some blind salamdras have eyes. These eyes have no use for these salamanders, so we can say that the eyes of the salamander is a vestigial structure.

According to the theory of evolution, organisms have undergone and undergo changes over time, with new species emerging from some common ancestor. Studying different groups of organisms, we realize several characteristics that serve as evidence for this theory. The presence of trace structures is one such evidence.

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds