What would be the effect on the polarity of the molecule formed when CCl4 has one Cl replaced by an H?

It will become polar.

Explanation:

Look the image below. I know it's terrible, but I'll explain it:

ΔE is the electronegativity. The higher is the ΔE of a substance, the more it can attracts electrons.

Cl has more electronegativity than C and H. But it has, of course, the same amount of another Cl.

So, when we have a tetrahedral space disposition such as in the left draw, all the Cl cancels the others eletrostatic force. However, when we replace one Cl for H, then we will have a dipole moment pointing to the Cl who face the Hydrogen, as the right draw. The appearance of a resulting dipole indicates the existence of a polar compound.

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.