Concept:Good electrical and thermal conduction in metals is caused by freely moving valence electrons.
Explanation:Alkali metals exhibit metallic bonding, where each atom loses its outermost electron.
These lost electrons form a shared mobile sea of delocalised electrons.
Because the electrons are not tied to any particular nucleus, they drift freely through the whole lattice.
When a voltage is applied, these delocalised electrons move in one direction and carry electric current.
When heat is applied, the same mobile electrons transfer kinetic energy quickly between particles.
This explains why alkali metals are excellent conductors of both heat and electricity.
Option B is incorrect because alkali metals are not found in the d-block.
Options C and D are incorrect because vibrating ions or simply being metals do not explain conduction.
Answer:A. contain delocalised electrons