Numerical answer · +4 / −1
The atomic number of Boron is 5 and Aluminium is 13. The number of electrons in Al³⁺ is x.
Answer and solution
Answer 10
Solution
Chemistry ma’am · 4 steps
The charge tells you how many electrons left: take 3 away from aluminium's 13.
- Neutral atom. A neutral atom has as many electrons as protons. Aluminium has atomic number 13, so a neutral Al atom has 13 electrons: 1s² 2s² 2p⁶ 3s² 3p¹.
- Read the charge. A charge of +3 means the atom has lost 3 electrons. The protons stay the same, so the nucleus keeps all 13.
electrons in Al³⁺ = 13 - 3 = 10
- Check. The three outer electrons (3s² 3p¹) are the ones lost, leaving 1s² 2s² 2p⁶. That is the neon configuration, which has 10 electrons. Boron's atomic number is not needed here.
- So. Al³⁺ has 10 electrons, so x = 10.
The common slip: 16. Adding the charge instead of subtracting it gives 16. A + charge means electrons were lost, not gained.
The idea to keep. Electrons in an ion = atomic number minus the charge. A positive charge means electrons were removed, and a negative charge means electrons were added. The protons never change.
Answer from the NTA final answer key. Solution by PrepWiser.