The formula of compound silver iodide is SI.

Almost all elements have chemical symbols in chemistry that begin with their name's initials. For instance, the chemical symbol for lithium is Li, while the symbol for hydrogen is H, and so on for practically all of the elements.
However, there are some exceptions to this. For instance, the chemical symbols for gold and iron are Au and Fe, respectively. Likewise, the chemical symbol for the second coinage metal, silver, is Ag.
This comes after the Latin word "Argentums," which means "silver."
Ag is the chemical name for the element.
The substance's valency is 1. As a result, it reacts with iodide to produce silver iodide.
The chemical symbol for silver iodide is AgI, not SI.
Therefore, the assertion made is false.

Hence, option 2 is correct.