Which of the following arrangements is in order of increasing metallic property?

Analyze the question: We need the order of increasing metallic property for the alkali metals Li, Na and K. Option C is incomplete ("K"), so we focus on the other options.

Concept: Metallic character depends on how easily an atom loses its outer electron(s) to form a positive ion.

• Going down a group, atomic radius increases.
• The outer electron is farther from the nucleus and is more shielded by inner electrons.
• So it is lost more easily, and metallic character increases down the group.

Solution: Group 1 order from top to bottom: Li (period 2), Na (period 3), K (period 4).

• Li has the smallest atomic size and holds its outer electron most tightly, so it is the least metallic.
• Na is in between.
• K has the largest size and loses its outer electron most easily, so it is the most metallic.

Increasing metallic property: Li < Na < K

Checking the options:

• A. Li < Na < K ✔ matches
• B. Na < Li < K ✘ (Li should come first)
• C. "K" ✘ (incomplete, not a valid arrangement)
• D. K < Li < Na ✘ (K is the most metallic, not the least)

Tip: For metals, reactivity and metallic character increase down a group and decrease across a period (left to right). Remember the alkali metals' reactivity with water: Li is gentle, Na is vigorous, K is violent (burns with a lilac flame). The more violent the reaction, the more metallic the element.