Which of the following represents the correct order of increasing first ionization enthalpy for Ca, Ba, S, Se and Ar?

Energy of an electron is given by $$E = - 2.178 \times {10^{ - 18}}J\left( {{{{Z^2}} \over {{n^2}}}} \right)$$. Wavelength of light required to excite an electron in an hydrogen atom from level n = 1 to n = 2 will be
(h = 6.62 × 10⁻³⁴ Js and c = 3.0 × 10⁸ ms⁻¹)

Experimentally it was found that a metal oxide has formula M_0.98O. Metal M, present as M²⁺ and M³⁺ in its oxide. Fraction of the metal which exists as M³⁺ would be

A gaseous hydrocarbon gives upon combustion 0.72 g of water and 3.08 g of CO₂. The empirical formula of the hydrocarbon is