The bond dissociation energy of B - F in BF₃ is 646 kJ mol^-1 whereas that of C - F in CF₄ is 515 kj mol^-1. The correct reason for higher B - F bond dissociation energy as compared to that of C - F is

The ionization enthalpy of hydrogen atom is 1.312 × 10⁶ J mol⁻¹. The energy required to excite the electron in the atom from n = 1 to n = 2 is

Which one of the following constitutes a group of the isoelectronic species?

The mean of the numbers a, b, 8, 5, 10 is 6 and the variance is 6.80. Then which one of the following gives possible values of a and b?