Henry Moseley studied characteristic X-ray spectra of elements. The graph which represents his observation correctly is

Given $$v=$$ frequency of $$\mathrm{X}$$-ray emitted

Z = atomic number

If the radius of the first orbit of hydrogen atom is $$\alpha_{0}$$, then de Broglie's wavelength of electron in $$3^{\text {rd }}$$ orbit is :

Which one of the following sets of ions represents a collection of isoelectronic species?

(Given : Atomic Number : $$\mathrm{F:9,Cl:17,Na=11,Mg=12,Al=13,K=19,Ca=20,Sc=21}$$)