To determine the number of valence electrons present in each atom, you need to look at the periodic table and identify the group (column) in which the element is located.
1. Oxygen (O) - Oxygen is in Group 16 (also known as Group VIA). Elements in this group have 6 valence electrons. So the answer is D. 6 valence electrons.
2. Aluminum (Al) - Aluminum is in Group 13 (also known as Group IIIA). Elements in this group have 3 valence electrons. So the answer is B. 3 valence electrons.
3. Neon (Ne) - Neon is in Group 18 (also known as Group VIIIA). Elements in this group have a full outer electron shell, meaning they have 8 valence electrons. So the answer is F. 8 valence electrons.
4. Silicon (Si) - Silicon is in Group 14 (also known as Group IVA). Elements in this group have 4 valence electrons. So the answer is C. 4 valence electrons.
5. Magnesium (Mg) - Magnesium is in Group 2 (also known as Group IIA). Elements in this group have 2 valence electrons. So the answer is G. 2 valence electrons.
6. Iodine (I) - Iodine is in Group 17 (also known as Group VIIA). Elements in this group have 7 valence electrons. So the answer is A. 7 valence electrons.
7. Lithium (Li) - Lithium is in Group 1 (also known as Group IA). Elements in this group have 1 valence electron. So the answer is H. 1 valence electron.
8. Nitrogen (N) - Nitrogen is in Group 15 (also known as Group VA). Elements in this group have 5 valence electrons. So the answer is E. 5 valence electrons.
Remember, the number of valence electrons determines an atom's chemical properties and how it will bond with other atoms.