To understand why the correct answer is option 'D', let's break down the process of inserting a new key into a B-tree index and analyze the maximum number of nodes that could be newly created in the process.

Understanding B-Trees:
- A B-tree is a self-balancing search tree that maintains sorted data and allows efficient insertion, deletion, and retrieval operations.
- It is commonly used as an index structure in large database tables to speed up searches.

Properties of B-Trees:
1. Every node has at most m children.
2. Every non-leaf node (except the root) has at least ⌈m/2⌉ children.
3. The root has at least 2 children if it is not a leaf node.
4. All leaves appear at the same level.

Given Information:
- The B-tree used as an index for the large database table has 7 levels, where the level of the root node is 0.

Analysis:
1. The number of levels in a B-tree indicates the number of levels of nodes from the root to the leaf nodes.
2. In this case, the B-tree has 7 levels, so there are 7 levels of nodes from the root to the leaf nodes.
3. Each level has a maximum number of nodes that can be present. Let's denote this maximum number as M.
4. The number of nodes at each level can be calculated using the formula: M = (m^(h+1) - 1) / (m - 1), where h is the level of the node and m is the order of the B-tree.
5. Since the level of the root node is 0 and we know the maximum number of nodes at level 0 (M), we can calculate the maximum number of nodes at each level up to level 7.
6. For level 0, M = (m^(0+1) - 1) / (m - 1) = (m - 1) / (m - 1) = 1.
7. For level 1, M = (m^(1+1) - 1) / (m - 1) = (m^2 - 1) / (m - 1).
8. Similarly, we can calculate the maximum number of nodes at each level up to level 7 using the formula M = (m^(h+1) - 1) / (m - 1).

Calculating the Maximum Number of Nodes:
- Let's assume the order of the B-tree (m) is not mentioned in the question. We'll calculate the maximum number of nodes for different values of m and find the option that satisfies the given condition.

For m = 2:
- For level 7, M = (2^(7+1) - 1) / (2 - 1) = 255.
- The maximum number of nodes that can be created in the process of inserting a new key is M - 1 = 255 - 1 = 254.

For m = 3:
- For level 7, M = (3^(7+1) - 1) / (3 - 1) = 21844.
- The maximum number of nodes that can be created in the process of inserting a new key is M - 1 = 21844 - 1 = 21843.

For m =