The block size in a file system plays a crucial role in determining the speed of file access. A smaller block size can lead to more efficient storage utilization for small files but may result in increased overhead for large files due to more blocks being allocated. On the other hand, a larger block size can improve the performance of accessing large files but may lead to wasted space for small files. Therefore, the block size choice depends on the expected file sizes and access patterns in a given system, balancing efficiency and performance accordingly.

The ACID property that ensures transactions are isolated from each other to prevent interference is Isolation. Isolation ensures that concurrent transactions do not see each other's intermediate states, thus preventing interference and maintaining data integrity.

The correct option is "Replication." Durability in ACID properties refers to the guarantee that once a transaction is committed, its changes will persist even in the event of system failures or crashes. Replication techniques, such as maintaining multiple copies of data across different storage locations or using backup servers, are employed to ensure data durability. These strategies help in recovering data and maintaining system availability despite hardware or software failures.

Representational State Transfer (REST) is an architectural style for distributed hypermedia systems. It emphasizes scalability, reliability, and the uniform interface between components. RESTful APIs use HTTP methods like GET, POST, PUT, DELETE to manipulate resources.

To calculate the total balance for each customer across multiple accounts in a banking application using SQL, you would typically use a JOIN statement with GROUP BY and SUM functions. This approach involves joining the tables that contain customer information and account balances, grouping the results by customer ID, and then summing up the balances to get the total balance for each customer. For example, if you have separate tables for customers and accounts, you would join these tables on the customer ID, group by customer ID, and use the SUM function to calculate the total balance. This method provides an efficient way to aggregate data across multiple accounts for each customer.

Git hooks are scripts that can be triggered by various Git events such as pre-commit, post-commit, pre-push, etc. These scripts allow developers to automate tasks or enforce certain rules and policies in the development workflow. For example, a pre-commit hook can be used to run code linting checks before allowing a commit, ensuring code quality standards are met. Similarly, a pre-push hook can be used to trigger unit tests before pushing changes to a remote repository, ensuring that only passing code is pushed. Git hooks provide a powerful way to customize and streamline the development process.

Singly linked lists only allow traversal in one direction, from head to tail, while doubly linked lists allow traversal in both directions, which enhances flexibility but comes with higher memory overhead.

The correct option is Content-Type. The Content-Type header in HTTP requests and responses specifies the media type of the data being sent or received. For example, it can indicate whether the data is in JSON, XML, HTML, or another format. This header helps the client and server understand how to handle the data appropriately.

Firewalls play a crucial role in web application security by filtering network traffic to identify and block malicious or unauthorized requests. They act as a barrier between the internet and the web server, inspecting incoming and outgoing data packets based on predefined rulesets. By analyzing factors such as IP addresses, port numbers, and packet contents, firewalls can detect and thwart various cyber threats, including DDoS attacks, SQL injection attempts, and unauthorized access attempts. This proactive defense mechanism helps prevent malicious entities from compromising the web application's integrity, ensuring continuous availability and data confidentiality for users.

The correct option is 'Top.' To implement a stack using arrays, we use a 'Top' pointer to keep track of the topmost element in the stack, allowing us to perform push and pop operations efficiently.