The issue is resolved after correcting at typo error in the code. Here is the updated code:

import pandas as pd

df= pd.read_excel(r"D:\SAMPLE EXCEL FILES\names.xlsx")

splitted = df['Names'].str.split()

first = splitted.str[0]
middle = splitted.str[1]
last = splitted.str[-1]

df['First Name'] = first
df['Middle Name'] = middle.mask(middle == last,'')
df['Last Name'] = last


print(df)