How many known elements have atoms, in their ground-state, with valence electrons whose quantum numbers are n = 5 and l = 1?.

Molarity of ions is 2.4 moles/kg

Explanation:

number of moles of Al(NO₃)₃ = 2 moles

Each Al(NO₃)₃ dissociates to release 3 nitrate ions (NO⁻₃)  

Al(NO₃)₃  > Al³⁺ + 3 NO⁻₃

therefore, 2 moles of Al(NO₃)₃  gives 6 moles of NO⁻₃ ions

Hence,

Molarity of ions = number of moles of ions / volume of solution

                          = 6 / 2.5

                          = 2.4 moles/kg