The potential of a hydrogen electrode (also known as the standard hydrogen electrode or SHE) is defined as zero by convention. In order to achieve this potential, a specific pressure of hydrogen gas (H2) is required at a given temperature. Let's break down the question and the answer to understand why option B is correct.

Given information:
- Temperature (T) = 298 K
- We need to find the pressure of H2 required to make the potential of H2-electrode zero in pure water.

Explanation:

To understand why the pressure of H2 is required to make the potential of the H2-electrode zero, we need to look at the half-cell reactions involved in the hydrogen electrode:

Half-cell reaction:
H2(g) ⇌ 2H+(aq) + 2e-

The electrode potential is determined by the ratio of concentrations of H+ ions to H2 gas. At standard conditions (1 atm pressure and 298 K), the concentration of H+ ions is 1 M (mol/L). In order to achieve a potential of zero, the ratio of concentrations should be 1:1.

Therefore, the pressure of H2 required to achieve this ratio can be calculated using the ideal gas law:

PV = nRT

Where:
P = pressure of H2 (in atm)
V = volume of H2 (in L)
n = number of moles of H2
R = ideal gas constant (0.0821 L.atm/mol.K)
T = temperature in Kelvin (298 K)

Calculation:

Since we are given that the pressure required is in atm, we can assume that the volume of H2 is 1 L (as the volume is not specified in the question). Using the ideal gas law equation, we can rearrange it to solve for P:

P = (nRT) / V

At standard conditions, 1 mole of any ideal gas occupies 22.4 L. Therefore, the number of moles of H2 required can be calculated as follows:

n = V / 22.4

Substituting the values of V and R into the equation, we get:

P = [(V / 22.4) x 0.0821 x 298] / V

Simplifying the equation, we find:

P = 0.036 atm

Therefore, the pressure of H2 required to make the potential of the H2-electrode zero in pure water at 298 K is 0.036 atm. This is equivalent to 10^-14 atm, which is the correct answer option B.

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