Data integrity in DB2 refers to maintaining the accuracy and consistency of data stored in the database. It ensures that data remains valid, reliable, and consistent throughout its lifecycle. This includes enforcing rules and constraints to prevent invalid data entry or modification, such as ensuring referential integrity and maintaining data consistency across multiple tables. Therefore, the correct option is to ensure the consistency of data. 

BLOB (Binary Large Object) data type is suitable for storing images in a DB2 database. BLOB allows for the storage of large binary objects, such as images, audio, or video files. It preserves the binary format of the data without any character encoding, making it ideal for non-textual data like images. 

Database backup in DB2 serves the purpose of preventing data loss in case of system failures. By creating backups, organizations can restore their data to a previous state if it gets corrupted or lost due to various reasons such as hardware failures, human errors, or disasters. This ensures data integrity and business continuity. 

db2restore is commonly used for database backup and recovery tasks in DB2. It allows users to restore the database to a previous state by applying archived log files or backup images. db2backup is used to create full or incremental backups of the database, while db2recovery is used to roll forward or roll back changes to the database. db2dart is a diagnostic tool used to analyze and repair corrupted database objects. 

Row-level locking in DB2 provides finer granularity for locking compared to table-level locking. With row-level locking, only the specific rows that are being modified are locked, allowing other transactions to access and modify different rows concurrently. This reduces contention and improves concurrency in the database. 

HADR (High Availability Disaster Recovery) in DB2 facilitates automatic failover by maintaining a standby server that automatically takes over in the event of a primary server failure. 

The correct option is 1. The STDDEV() function in DB2 returns NULL when applied to a column with NULL values. It does not include NULL values in the calculation of standard deviation. 

User-defined functions in DB2 can contribute significantly to performance tuning efforts by leveraging the query optimizer. When properly designed and utilized, UDFs can enable the optimizer to generate efficient execution plans, leading to improved query performance. This allows DBAs to streamline database operations and enhance overall system performance. 

DB2 handles invalid XML characters within tags by escaping them with equivalent HTML entities. This ensures that the XML remains well-formed and can be processed correctly by XML parsers. Escaping involves replacing characters like '<' and '>' with their corresponding HTML entities such as '<' and '>'. 

The correct answer is option C. The installation directory in DB2 is commonly known as the DB2_ROOT directory. This directory contains all the files and subdirectories required for the DB2 installation process. 

XMLTABLE is a powerful feature in DB2 that allows a DBA to generate XML output from query results while providing flexibility in customizing the format according to specific requirements. With XMLTABLE, the DBA can define the structure of the XML output, including elements, attributes, and namespaces, thus achieving the desired format customization directly within the database. This feature streamlines the process of generating customized XML output from DB2 query results. 

In disaster recovery planning, "RPO" stands for Recovery Point Objective. RPO refers to the maximum acceptable amount of data loss measured in time before a disaster occurs, which determines the frequency of data backups.