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Question:

The reduction potential of hydrogen half-cell will be negative if:

p(H2)=1atom and[H+]=2.0M

p(H2)=2atm and[H+]=1.0M

p(H2)=2atm and[H+]=2.0M

p(H2)=1atm and[H+]=1.0M

Solution:

2H⁺+2e⁻→H₂(g)
EH⁺/H₂=E⁰H⁺/H₂ - (0.0592/2)log(PH₂/[H⁺]²)=0 - (0.0592/2)log(PH₂/[H⁺]²)
For the negative value of EH⁺/H₂
By PH₂/[H⁺]² should be >1 i.e PH₂>[H⁺]²