1. The atomic mass of the most common isotope of magnesium is . 2. The element with an atomic number of 4 is .

3. exist in orbitals around the nucleus.

4. Oxygen has protons in the nucleus.

5. An isotope of an element has the same number of protons but a different number of .

I just did this for Penn Foster and the correct answers are:
1. 24
2. beryllium
3. Electrons
4. 8
5. neutrons
Hope this helps someone! :)

humans can cause extinction of a species through overharvesting, pollution, habitat destruction, introduction of invasive species (such as new predators and food competitors), overhunting, and other influences. explosive, unsustainable human population growth is an essential cause of the extinction crisis.

explanation:

i didn't have the answer choices , but i tried my best.

b brown mice / white sand dunes

c. heat from the poles back down towards the equator.