Question

In an aqueous solution which substance yields hydrogen ions as the only positive ion *

Answer 1

The question is incomplete. Complete question is
In an aqueus solution, which substance yields hydrogen ions as the only positive ions in the solution? 1)NaH 2)HCOOH 3)LiOH 4) CH3CH2OH?
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Answer: Correct answer is option 2, HCOOH

Reason: 
HCOOH is a formic acid. When mixed in water, it undergoes dissociation which can be represented as

HCOOH         ↔           HCOO-       +            H+

The compound NaH, will generate hydride ion (H-), while LiOH is an ionic compound, hence when dissolved in water it generated OH- ions. The compound CH3CH2OH is named as ethyl alcohol. This compound donot dissociate in aqueous medium.