Na is sodium And is highly reactive as comes in top of the reactivity series it is highly endothermic.

Understanding Metallic Character
Metallic character refers to the tendency of an element to lose electrons and form positive ions (cations). Generally, metallic character increases as you move down a group in the periodic table and decreases as you move from left to right across a period.
Elements in the Question
- Na (Sodium): An alkali metal located in Group 1.
- Mg (Magnesium): An alkaline earth metal located in Group 2.
- Al (Aluminum): A post-transition metal located in Group 13.
- Si (Silicon): A metalloid located in Group 14.
Comparison of Metallic Character
- Sodium (Na):
- Belongs to Group 1, known for having a high metallic character.
- Easily loses one electron to form Na+ ion.
- Exhibits typical metallic properties such as luster, malleability, and conductivity.
- Magnesium (Mg):
- Located in Group 2, has a lesser metallic character compared to sodium.
- Loses two electrons to form Mg2+ but is still metallic in nature.
- Aluminum (Al):
- Found in Group 13, has some metallic character but is more non-metallic than sodium and magnesium.
- Can lose three electrons but shows a mix of metallic and non-metallic properties.
- Silicon (Si):
- A metalloid in Group 14, has a significantly lower metallic character.
- Does not readily lose electrons as metals do, exhibiting more non-metallic behavior.
Conclusion
Among the options given, sodium (Na) is the most metallic element due to its position in the periodic table and its ability to easily lose an electron. Thus, option 'A' is the correct answer.