What is a linear collection of data elements where the linear node is given by means of pointer called?

$2.$ What operation is performed more efficiently by doubly linked list than by singly linked list?

$3.$ Consider an implementation of unsorted singly linked list. Suppose it has its representation with a head and tail pointer. Given the representation, which of the following operation can be implemented in O$(1)$ time?

i$)$ Insertion at the front of the linked list

ii$)$ Insertion at the end of the linked list

iii$)$ Deletion of the front node of the linked list

iv$)$ Deletion of the last node of the linked list

$4.$ Consider an implementation of unsorted singly linked list. Suppose it has its representation with a head pointer only. Given the representation, which of the following operation can be implemented in O$(1)$ time?

i$)$ Insertion at the front of the linked list