Answer:
n=1 holds two electrons and n=2 holds eight electrons.
Explanation:
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In this case, since the atomic number of aluminum is 13, its electron configuration is:

In such a way, we can see that the level n=1 is filled with two electrons since the subshell s is able to hold two electrons and the level n=2 is also filled but with eight electrons as s holds two whereas p holds 6. Moreover, n=3 is holding three electrons.
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Answer: Nuclei combine to form a heavier nucleus, releasing energy.
Explanation: e.g two deuterium nucleus (Hydrogen-2 isotopes) forms an He nucleus and energy is released.