The correct decreasing order for metallic character is:

🧠 Metallic character grows down a group AND grows leftward across a period — apply both rules Metallic character is "how easily an atom loses an electron". Bigger atom (down) and fewer protons relative to size (left) → easier to lose → more metallic.

🗺️ Place each element Na: Group 1, Period 3 — leftmost, biggest. Most metallic. Mg: Group 2, Period 3 — one column right of Na. Slightly less metallic. Be: Group 2, Period 2 — same group as Mg but one period above. Smaller, less metallic than Mg. Si: Group 14, Period 3 — metalloid. Much less metallic than any of the alkali/alkaline earth metals. P: Group 15, Period 3 — non-metal. Least metallic.

Two comparisons to settle: Na vs Mg (same period): Na is left → Na > Mg. ✓ Mg vs Be (same group): Mg is below Be → Mg > Be. ✓

Order: $\ce{Na} > \ce{Mg} > \ce{Be} > \ce{Si} > \ce{P}$.

⚠️ The trap Don't compare Be and Na directly using the period-trend ("Be is to the right of Na in Period 2 → less metallic"). They are in different periods. The cleanest way is to do pair comparisons within the same period or same group. Keep one variable fixed at a time.

$\boxed{\text{Answer: (a)}}$