Question

Which among the following metals requires radiation of the shortest wavelength to cause emission of electrons?

• A. $Na$
• B. $K$
• C. $Mg$
• D. $Ca$

Answer 1

The correct option is C $Mg$

Ionisation energies of IIA group elements are greater than IA group
$(Mg,Ca)>(Na,K)$
Also,among IIA group elements first ionisation energy gradually decreases as we descend the group.
$Mg>Ca>Na>K$
Since energy is inversely proportional to wavelength, a radiation of the shortest wavelength means that energy should be high. The one with the highest ionisation energy among the given elements is $Mg$.