Above question is incomplete. Complete question is:
Which 0.1-molar aqueous solution is the best conductor of electricity? (1) H2S (2) H2SO4 (3)HF (4)H3PO4?
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Answer: Correct answer is option 4, i.e. H3PO4.
Reason:
Each molecule of H3PO4 on dissociation will generate 4 ions (three H+ ions and one PO4 3-ion). On other hand, H2SO4 and HF will generate three and two ions respectively. H2S is a covalent compound, and will not generate any ions in solution. Due to largest number of ions, 0.1 M H3PO4 solution will have maximum conductivity. Hence, it will be the best conductor of electricity.