Question

Which of the following is a poor conductor of electricity?
A. Distilled water
B. Tap water
C. Sea water
D. Drinking water

Answer 1

To conduct electricity through water, it must carry the ions (cations and anions) which are the charge carriers. The conductivity of water directly depends on the concentration of dissolved ions in solution. For electricity to travel through a liquid, movement in charge must occur throughout and among the liquid.

Complete answer:
Option A: Distilled water is a good insulator due to its good ionic solvent which permits them to dissolve ionic compounds effectively with no problem. Since it contains a large number of dissolved particles it can't turn into a good conductor of electricity. In distilled water there are no impurities, there are no ions, there are just neutral (no charge) water atoms and these neutral particles don't have charge. So, distilled water doesn't conduct electricity.
Option B: Tap water conducts electricity since there are small amounts of calcium and magnesium salts break down in it, pure water (refined or deionized) has nothing at all in it that can conduct electricity. This is because that water itself isn't a conductor. In any case, when one dissolves ionic compounds, for example, salts, the ions turn out to be approximately bound to one another which makes tap water a good conductor of electricity.
Option C: Sea water contains a large amount of dissolved salts in it. Hence, the electrical conductivity of seawater is more than drinking water. Electricity can pass through the sea water as it contains common salt (sodium chloride $NaCl$), ions being charged particles can conduct electricity. Sea water has a relatively high number of sodium and chloride ions.
Option D: High quality deionized water has a conductivity of about $0.5\mu S/cm$at${{25}^{o}}C$, typical drinking water is in the range of $200-800 \mu S/cm$. Drinking water does also conduct electricity but not more than seawater.
Pure water (distilled water) is certainly not a good conductor of electricity.

Hence, the correct option is option (A).

Note: The units of conductivity are Siemens per meter$S/m$. Deionized water by its nature has very less ions. Its conductivity is around $5.5\mu S/m$. Standard distilled water in equilibrium with carbon dioxide of the air has a conductivity of around $10\times {{10}^{-6}}{{W}^{-1*}}{{m}^{-1}}\left( 20dS/m \right)$. Since the electrical flow is moved by the ions in solution, the conductivity increments as the concentration of ions increments.