Identifying the element with highest melting point and lowest electrical conductivity in each set

Steps:

• Recall melting points: Mg (650°C), Al (660°C), Si (1414°C), Na (98°C), P (44°C), S (115°C), Cl (-101°C).
• Recall electrical conductivities: Metals (Na, Mg, Al) are good conductors; metalloid Si is a poor conductor (semiconductor); non-metals (P, S, Cl) are insulators with very low conductivity.
• For set A, Si has the highest MP (1414°C) and lowest conductivity (semiconductor vs. metals Mg/Al).
• Check other sets: No single element meets both criteria, as high-MP elements lack lowest conductivity or vice versa.

Why A is correct:

• Silicon's covalent network structure gives it the highest melting point among group 14 elements and low electrical conductivity as a semiconductor, unlike metallic Mg and Al.

Why the others are wrong:

• B: Si has highest MP but P has lower conductivity than Si.
• C: Al has highest MP but S has the lowest conductivity.
• D: Si has highest MP but Cl and P have lower conductivity than Si.

Final answer: A