A word processor is a software application that allows users to create, edit, format, and print documents. It is primarily used for typing and formatting text-based documents.

The correct answer for this question is option 'D' - Type a biography. Let's understand why:

1. Introduction to a Word Processor:
- A word processor is a software program that allows users to create, edit, and format text-based documents.
- It provides various tools and features to manipulate text, such as changing fonts, adjusting spacing, adding headers and footers, and inserting images.

2. Purpose of a Word Processor:
- The primary purpose of a word processor is to facilitate the creation of documents that primarily consist of text.
- It is widely used for various purposes, including writing essays, letters, reports, articles, and even biographies.

3. Typing a Biography:
- Biographies are written accounts of a person's life, capturing their achievements, experiences, and significant events.
- A word processor is an ideal tool for typing a biography because it allows users to easily type and format the text.
- It offers features like spell check, grammar check, and the ability to insert images, which can enhance the overall presentation of the biography.
- Additionally, a word processor enables easy editing and revising of the content, ensuring that the final biography is error-free and well-structured.

4. Other Options:
- Option 'A' - Keep an account of money spent: A word processor is not typically used for financial record-keeping. Specialized software or spreadsheets are more suitable for this purpose.
- Option 'B' - Do a computer search in media center: A word processor is unrelated to performing computer searches in a media center. Internet browsers or search engines are used for this task.
- Option 'C' - Maintain an inventory: A word processor is not designed for inventory management. Dedicated inventory management software or spreadsheets are commonly used for this purpose.

In conclusion, a word processor is most commonly used to type and format text-based documents, making it an appropriate tool for typing a biography.