Correct answer is : A

Refer to -  https://www.pythoneasy.com/python-programming-tutorial/python-list-methods

Correct answer is : B

s.insert(3, 12) will insert 12 at index 3. So the result will be [23, 24, 26, 12, 56, 78]

Correct answer is : A

s.count()     counts number times an element present inside the list

Correct answer is : C

s1.sort() sorts elements of the list in place, but does not return anything means returns None

so s1 will be [6, 12, 16, 21, 31, 72, 91].and s2 will be None

Correct answer is : D

s1.index(45) gives the index of element 45 in s1 which is 3 

Correct answer is : D

s.clear() - removes all elements from the list , so s.index('python3') will raise a ValueError as follows.

>>> s = ['python2' , 'python3', 'java8', 'perl5', 'java9']
>>> s.clear(), s.index('python3')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: 'python3' is not in list
>>>

Correct answer is : A

s.remove(23) removes 23 only once from the list

Correct answer is : C

s.extend() takes any iterable and adds to the list.

So the result will be [45, 78, 25, 56]

Correct answer is : A

s[3] will give 12 and s.pop() will give 38 . 

12 + 38 will be 50 

Correct answer is : C

s.append([56]) will add [56] which is a list to "s" , and s.extend([87, 12]) will add individual elements 87 and 12 to "s".

So the result will be [19, 12, 87, [56], 87, 12]