The group having isoelectronic species is:

$$\Delta $$U is equal to :

Which of the following species is not paramagnetic?

The radius of the second Bohr orbit for hydrogen atom is:
(Planck’s Const. h = 6.6262 × 10^-34 Js; mass of electron = 9.1091 × 10^-31 kg; charge of electron (e) = 1.60210 × 10^-19 C; permittivity of vacuum ($${\varepsilon _0}$$) = 8.854185 × 10^-12 kg^-1 m^-3 A²)