How did you know whether a substance conducted electricity and explain the observed electrical conductivity in each of the following substances: a) solid lead(II) bromide, b) molten lead(II) bromide, c) solid sodium chloride, d) aqueous sodium chloride, e) glucose solution?

1: A solution conducts electricity if the bulb glows brightly, dimly, or not at all when electrodes are dipped in it and connected to a battery and bulb.

If the bulb glows, the solution conducts electricity.

2a: Aqueous HCl is a strong acid that completely ionizes in water to produce a large number of free $\ce{H+}$ and $\ce{Cl-}$ ions.

$\ce{HCl_{(aq)} -> H+_{(aq)} + Cl-_{(aq)}}$

These mobile ions carry electric current, so the bulb glows brightly.

\boxed{Aqueous HCl conducts due to complete ionization into $\ce{H+}$ and $\ce{Cl-}$ ions.}

2b: Solid lead(II) bromide is an ionic compound, but the $\ce{Pb^2+}$ and $\ce{Br-}$ ions are held fixed in the crystal lattice and cannot move.

No free mobile ions are present to carry electric current.

\boxed{Solid $\ce{PbBr2}$ does not conduct as ions are immobile in the lattice.}

2c: Glucose solution contains neutral glucose molecules that do not ionize or dissociate into ions in water.

No free ions are present to conduct electricity.

Glucose solution does not conduct as it is a non-electrolyte (no ions).

2d: Dilute sulphuric acid is a strong acid (dibasic) that ionizes stepwise to produce $\ce{H+}$ and $\ce{HSO4-}$ (and further $\ce{SO4^2-}$) ions.

$\ce{H2SO4_{(aq)} -> H+_{(aq)} + HSO4-_{(aq)}}$

$\ce{HSO4-_{(aq)} <=> H+_{(aq)} + SO4^2-_{(aq)}}$

Mobile ions carry current, so the bulb glows.

\boxed{Dilute $\ce{H2SO4}$ conducts due to ionization into $\ce{H+}$, $\ce{HSO4-}$, and $\ce{SO4^2-}$ ions.}