Question

Which of the following metals require radiation of highest frequency to cause emmission of electrons?

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

Answer 1

Answer: (B)

$Mg$

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.

$Mg>Ca>K>Na$

$Mg$ requires high-frequency radiation to cause the emission of electrons.