Identify the least stable ion amongst the following

Identify the correct order of acidic strengths of CO₂, CuO, CaO, H₂O

If the nitrogen atom has electronic configuration 1s⁷, it would have energy lower than that of the normal ground state configuration 1s²2s²2p³, because the electrons would be closer to the nucleus. Yet 1s⁷ is not observed because it violates

Rutherford's experiment, which established the nuclear model of the atom, used a beam of