The essential condition which is checked before insertion in a linked queue is?

Before inserting an element in a linked queue, the essential condition that is checked is whether the queue is full or not.

Here are the steps:

1. Check if the queue is full. In a linked queue, this condition is checked by seeing if there is enough memory to allocate for a new node. If there is not enough memory, then the queue is considered full.

2. If the queue is not full, then create a new node and insert the data into the new node.

3. If the queue is empty, then set the front and rear pointers to the new node.

4. If the queue is not empty, then add the new node at the end of the queue and update the rear pointer.

5. Finally, increment the size of the queue.

So, the essential condition checked before insertion in a linked queue is the availability of memory for a new node.