Consider the queues $Q_1$ containing four elements and $Q_2$ containing none (shown as the Initial State in the figure). The only operations allowed on these two queues are Enqueue($Q$, element) and Dequeue($Q$). The minimum number of Enqueue operations on $Q_1$ required to place the elements of $Q_1$ in $Q_2$ in reverse order (shown as the Final State in the figure) without using any additional storage is

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Initially, $Q_1 = [1, 2, 3, 4]$ and $Q_2 = []$. To reverse the elements of $Q_1$ using $Q_2$ with the minimum number of Enqueue operations, we perform the following steps: 1. Dequeue element 1 from $Q_1$ and Enqueue it to $Q_2$. $Q_1 = [2, 3, 4]$, $Q_2 = [1]$ 2. Dequeue element 2 from $Q_1$ and Enqueue it to $Q_2$. $Q_1 = [3, 4]$, $Q_2 = [1, 2]$ 3. Dequeue element 3 from $Q_1$ and Enqueue it to $Q_2$. $Q_1 = [4]$, $Q_2 = [1, 2, 3]$ 4. Dequeue element 4 from $Q_1$ and Enqueue it to $Q_2$. $Q_1 = []$, $Q_2 = [1, 2, 3, 4]$ The elements are now in reverse order in $Q_2$, so the minimum number of Enqueue operations on $Q_1$ is: $$ \boxed{0} $$

LIST I	LIST II
C. Deletion operation	IV. Dequeue
A. Insertion in a queue at	I. FRONT
B. Deletion in a queue at	III. REAR
D. Insertion operation	II. Enqueue

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