Consider the equation below

plz help don't just give answer explain so i can understand

The equilibrium constant : Kc=[CO₂]

The equilibrium constant is the value of the product in the equilibrium state of the substance in the right (product) divided by the substance in the left (reactant) with the exponents of each reaction coefficient  

The equilibrium constant is based on the concentration (Kc) in a reaction  

pA + qB -----> mC + nD  

Solid (s) and liquid (l) are not included in the calculation of Kc(only aq-aquoeus and g-gas)

From reaction

CaCO₃(s)⇔CaO(s)+CO₂(g)

Because CaCO₃ and CaO are solid, only CO₂ is included in the calculation

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

if it's not useful, feel free to report for mistake in answer.