What is Helmholtz double layer?

Write notes on i. Brownian movement ii. Tyndall effect iii. Helmholtz double layer

When an excess and a very dilute aqueous solution of KI is added to a very dilute aqueous solution of silver nitrate, the colloidal particles of silver iodide which are associated with Helmholtz double layer are

When an excess of a very dilute aqueous solution of KI is addd to a very dilute aqueous solution of silver nitrate, the colloidal particles of silver iodide are associated with which of the following Helmholtz double layer ?