Each atom of protium has one
proton, no neutrons, and one electron. each
atom of deuterium has one proton, two
neutrons, and one electron. are these the
ame or different elements? why?

That depends on which hydrogen isotope you're referring to.

Hydrogen has three naturally occuring isotopes, protium, deuterium, and tritium.

Explanation:

Isotpes are elemens that have the same number of protons and electrons, but different numbers of neutrons.

So, an isotope of hydrogen will always have one proton in the nucleus and one electron surrounding the nucleus.

As you can see in the image, each of those three naturally occuring isotopes has a different number of neutrons in the nucleus.

Protium, which is usually called hydrogen, has one proton, one neutron, and one electron;

Deuterium has one proton, two neutrons, and one electron;

Tritium has one proton, three neutrons, and one electron.

An atom's valence shell is simply the outermost energy level that is occupied by electrons. For all three hydrogen isotopes, the valence shell, which is the only shell occupied, will contain one electron.

you are certainly talking about this picture:

a: is the label of the white square, it is showing the  replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication 

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes  the dna with the dna template and increases  the processivity of the enzyme. ==>   stops polymerase from falling off the  template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built  in the opposite sense of the helicase, so dna will be built in fragments ==> built  fragments from 5' to 3 joins

and finally f: is the enzyme that builds  the new dna strand (dna polymerase) ==>   adds nucleotides to make a new dna helix.

credit: gradman555p98x9p

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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.