Q.Consider the elements B, Al, Mg and K predict the correct order of metallic character:
a. B > Al > Mg > K
b. Al > Mg > B > K
c. Mg > Al > K > B
d. K > Mg > Al > B

Step 1. Locate each element. B: period 2, group 13. Al: period 3, group 13. Mg: period 3, group 2. K: period 4, group 1.

Step 2. Recall the metallic-character trend. Metallic character increases down a group and decreases across a period (section 7.5.3.2).

Step 3. Rank K first. K is in group 1 (the most metallic group among these four) and in period 4 (the lowest/largest among these four) — so K is the most metallic.

Step 4. Rank the rest. Mg (group 2, period 3) is next most metallic. Al (group 13, period 3) is less metallic than Mg (same period, but group 13 is further right/more nonmetallic-leaning than group 2). B (group 13, period 2) is the least metallic — same group as Al but one period UP, meaning smaller size and higher effective nuclear charge/electronegativity, and B is in fact classified as a metalloid, not a metal at all.

Step 5. Assemble the order. K > Mg > Al > B.

Ranking four elements by combined period (across-period decrease) and group (down-group increase) position

• Ranking only by group number or only by period, ignoring that both trends must be combined here since the four elements differ in both.
• Placing B above Al, forgetting metallic character decreases going UP a group (B is above Al in group 13).