You can use the LINQ method
Intersect[
^] to easily find elements in both arrays:
var inBothArr1AndArr2 = arr1.Intersect(arr2);
var inBothArr1AndArr3 = arr1.Intersect(arr3);
var inBothArr1AndArr4 = arr1.Intersect(arr4);
Now you have three
IEnumerable<T>
s. Do with their contents what you need to do.
[Edit]
From your comment, it appears you want to do this one-by-one. That's possible too:
for (int i = 0; i < arr1.Length; i++)
{
if (arr2.Contains(arr1[i]))
{
}
}