To understand why the number of components in G should lie between 7 and 19 when a vertex is deleted, let's break down the problem step by step.

1. Understanding the Terminology:
- A graph is a collection of vertices (or nodes) and edges that connect these vertices.
- A simple graph is an undirected graph with no self-loops or multiple edges between the same pair of vertices.
- Components in a graph refer to the subgraphs that are disconnected from each other. In other words, they are the separate clusters or groups of vertices within the graph that are not connected to any other group.

2. Given Information:
- G is a simple graph with 20 vertices.
- G has 8 components.

3. Initial Scenario:
- Since G has 8 components, it means that there are 8 separate clusters of vertices that are disconnected from each other.
- Let's assume these components as C1, C2, C3, ..., C8.

4. Deleting a Vertex:
- Now, if we delete a vertex from G, we need to consider the possible scenarios that can arise.
- Deleting a vertex from a component can either:
a) Disconnect the component into smaller components, or
b) Leave the component as it is if the deleted vertex is not a part of that component.

5. Worst-case Scenario:
- To find the minimum and maximum number of components that can arise after deleting a vertex, we consider the worst-case scenario.
- The worst-case scenario occurs when the deleted vertex is a part of every component.
- In this case, deleting the vertex will disconnect all the components and create 8 new components.
- So, the minimum number of components after deleting a vertex is 8.

6. Best-case Scenario:
- To find the maximum number of components that can arise after deleting a vertex, we consider the best-case scenario.
- The best-case scenario occurs when the deleted vertex is not a part of any component.
- In this case, deleting the vertex will not affect the existing components, and the number of components will remain the same.
- So, the maximum number of components after deleting a vertex is 8.

7. Conclusion:
- Therefore, after deleting a vertex in G, the number of components in G should lie between 8 (minimum) and 8 (maximum).
- In other words, the number of components in G should be exactly 8, regardless of which vertex is deleted.

Hence, the correct answer is option 'C': 7 and 19.