The correct order of metallic character is :

Solution

Chemistry ma’am · 4 steps

Metallic character means losing electrons easily, so rank by how low the ionisation enthalpy is.

1. What to compare. A metal is an element that gives away its valence electrons easily. The lower the ionisation enthalpy, the more metallic the element.

   Element	Position	First ionisation enthalpy	Metallic character
   K	Group 1, period 4	419 kJ mol⁻¹	highest
   Ca	Group 2, period 4	590 kJ mol⁻¹	middle
   Be	Group 2, period 2	899 kJ mol⁻¹	lowest

2. K versus Ca. Both are in period 4. Calcium has one more proton pulling on the same 4s shell, so its electrons are held more tightly. Potassium also has to lose only one electron to reach a noble gas configuration, so K is more metallic.
3. Ca versus Be. Both are in group 2. Beryllium is two periods higher, so its 2s electrons sit much closer to the nucleus and are hard to remove. Be is the least metallic of the three.
4. So. The order is K > Ca > Be, which is option (c).

The idea to keep. Metallic character rises down a group and falls across a period from left to right. It runs exactly opposite to ionisation enthalpy.

Answer from the NTA final answer key. Solution by PrepWiser.