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Correct statement about Helmholtz electrical double layer is
I) It is a combination of two layer of similar charges around colloidal sol
II)It is a combination of two layers of opposite charges around the colloidal sol
III)In it 1st layer of ions is diffused while 2nd layer of ions is fixed
IV) The potential difference between the fixed layer and the diffused layer is called zeta potential
A) II & IV
B) I & III
C) III & IV
D) I & IV

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Last updated date: 13th Jun 2024
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Answer
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Hint: Helmholtz electrical double layer consists of two layers of opposite polarity interfaced between an electrode and an electrolyte. The potential difference between the dispersion medium and stationary fluid is called the zeta potential.

Complete answer:
Helmholtz double layer is the combination of two layers of opposite charge around the colloidal particle. It represents the accumulation of electrical charges present at the boundaries of an electrolyte and electrode when they get in contact with each other. An electric field is created by the surface charge which affects the ions in the bulk of the liquid. The electric surface charge gets screened by the counter charge created by the thermal motion of ions. The electric charge along the screening diffuse layer will be equal in magnitude with that of the surface charge and will be of opposite polarity. Hence the complete structure will be neutral.
As the separation of charge is a seat of potential, there develops a change in potential due to the presence of opposite charges along the fixed and diffused part of the double layer in the same manner as in a capacitor. This potential difference between the fixed layer and diffused layer of opposite charges is called the electrokinetic potential or zeta potential.
Hence the correct statements are
II. It is a combination of two layers of opposite charges around the colloidal sol
IV. The potential difference between the fixed layer and the diffused layer is called zeta potential

$\therefore$ Option A is the answer.

Note: The double layer usually refers to parallel layers of charge surrounding an object. The first layer comprises the surface charge which includes ions absorbed on the object as a result of chemical interactions whereas the second layer consists of ions attracted to the surface charge.