Lustre, electrical and thermal conductivity of metals can be explained by the theory of:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Sea of free electrons
In a metallic solid every metal atom gives up its valence electrons. The positive metal ions (kernels) stay at the lattice points, and the released electrons spread through the whole crystal as a sea of mobile electrons that holds the ions together.
The mobile electrons of this electron sea account for the lustre and the high electrical and thermal conductivity of metals.
Why the other options are incorrect
Option (1) dipole-dipole interactions — Incorrect. These hold polar molecular solids such as solid HCl and \( \ce{SO2} \); such solids are insulators.
Option (2) Coulombic (electrostatic) forces — Incorrect. These hold ionic solids; their ions cannot move in the solid, so ionic solids conduct only when molten or dissolved.
Option (4) London forces — Incorrect. These weak dispersion forces hold non-polar molecular solids such as Ar and \( \ce{CCl4} \), which are soft insulators with low melting points.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Metallic Solids
