Answer:
6. Al
7. 3
Step-by-step explanation:
When looking at ionization energies to find the number of valence electrons, look for big jumps in ionization energy. The jump from first to second is big, but it's only about 1200 kj/mole (which is considered to be a medium small jump). This means that the first electron and second electrons are both likely valence electrons (since the energy needed to remove them is relatively small). From second to third, the change in ionization energy is less than 1000 kj/mole. Since the third ionization energy is also quite small, the third electron is also likely to be a valence electron. However, looking at the change in ionization energy from the third to the fourth, the jump/difference in ionization energy is nearly 9000 kj/mole! That's 7 to 9 times the amount of the previous jumps. From this, we can reasonably assume that this is a core electron, which takes lots of energy to remove from an atom. Therefore, the fourth electron is a core electron, and this atom only has 3 valence electrons. Now, we can answer question 7. It is C. From this, look at number 6. Na only has 1 valence electron, Mg only has 2 valence electrons, Si has 4 valence electrons, and only Al has 3 valence electrons. Since this mystery element X has 3 valence electrons and Al also has 3 electrons, Al is the most fit for the data given. So the answer to number 6 is C) Al
tl;dr there is a jump of ionization energy from the 3rd ionization energy to the 4th ionization energy so that means that the 4th electron is a core electron, and the element only has 3 valence electrons. Al has 3 valence electrons