The correct answer is option 'C' - Trial Balance.

The Trial Balance is prepared to ascertain the arithmetical accuracy of posting and balancing in an accounting system. It is a statement that lists all the accounts and their balances at a particular point in time. The purpose of the trial balance is to ensure that the total debits equal the total credits, which indicates that the accounting entries have been recorded correctly.

Here is a detailed explanation of why the Trial Balance is used to ascertain the arithmetical accuracy of posting and balancing:

1. Purpose of the Trial Balance:
- The primary purpose of the trial balance is to check the mathematical accuracy of the ledger accounts.
- It ensures that the total debits and total credits recorded in the ledger are equal.
- If the trial balance does not balance, it indicates that there are errors in the posting or balancing of accounts.

2. Process of Preparing a Trial Balance:
- The trial balance is prepared by listing all the ledger accounts and their respective balances.
- The balances are classified into debit and credit columns.
- The total of the debit column is compared to the total of the credit column.
- If the totals match, the trial balance is said to be in balance. If they don't match, there is an error somewhere in the accounts.

3. Identifying Errors through the Trial Balance:
- If the trial balance does not balance, it suggests that there are errors in the ledger accounts.
- Some common errors that can be identified through the trial balance include:
- Errors in recording transactions in the ledger.
- Errors in posting entries from the journal to the ledger.
- Errors in totaling or balancing accounts.
- Errors in calculating account balances.
- Errors in transferring balances from one account to another.

4. Correcting Errors:
- Once errors are identified through the trial balance, they need to be corrected.
- The trial balance helps in locating the accounts where errors have occurred.
- By reviewing the ledger accounts and the corresponding journal entries, the errors can be rectified.

In conclusion, the Trial Balance is prepared to ascertain the arithmetical accuracy of posting and balancing in an accounting system. It serves as a tool for identifying errors in the ledger accounts and ensuring that the total debits equal the total credits.

Trial balance because it is prepared after all the accounts which have been prepared to check the accuracy of accounts. the main purpose of preparing trial balance is to check the accuracy or error