Why output is different for both scenario?

Question

Scenario 1
arr = [[]]*3
arr[0].append(7)
print(arr)

Scenario 2
arr1=[[],[],[]]
arr1[0]=7
print(arr1)

Answer 1

sc1: arr is an arr if three identical arrays (memory address is equal)
sc2 arr is an array of three different arrays

Answer 2

list is array

Answer 3

what if it is list?