What will happen,if we run below code?

Dim dict As New Dictionary(Of String, Integer)
dict.Add("1", 100)
dict.Add("1", 200)

Answer:

When we run above code,then it will throw an error saying that

An item with the same key has already been added.

Because we know that Dictionary have Unique key,it can not be Duplicate.

Always check if key is duplicate:

if (!dict_names.ContainsKey("Key"))

{

    //add keys into Dictionary

}