The wavelength of the radiation emitted when in a hydrogen atom electron falls from infinity to stationary state 1, would be (Rydberg constant = 1.097 $$\times$$ 10⁷ m^-1)

Which one of the following sets of ions represents the collection of isoelectronic species? (Atomic nos. : F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)

Which one of the following ions has the highest value of ionic radius?

Among Al₂O₃, SiO₂, P₂O₃ and SO₂ the correct order of acid strength is