JDBC (Java Database Connectivity) allows Java applications to communicate with DB2 databases through API calls. JDBC provides a set of interfaces and classes for executing SQL queries, managing connections, and processing results. 

In an ERD, a double-lined rectangle represents a strong entity. A strong entity is one that exists independently of other entities and has its own unique identifier. It is not dependent on any other entity for its existence. 

The correct option is 1. The VARIANCE() function in DB2 calculates the variance of the values in a column, which represents how much the values in the column deviate from the mean value of the column. 

When selecting an encryption algorithm in DB2, key considerations include the strength of encryption, performance impact, and compatibility with regulatory requirements. These factors ensure data security and compliance. 

Transitive dependency occurs in a relation when a non-prime attribute depends on another non-prime attribute, which, in turn, depends on the primary key. This dependency chain indicates that the non-prime attribute is indirectly dependent on the primary key through another non-prime attribute, violating the rules of normalization. 

This scenario illustrates a One-to-Many relationship in the ERD. It implies that one employee can have multiple dependents, but each dependent can only be associated with one employee. 

This scenario represents a One-to-Many relationship in the ERD. In a One-to-Many relationship, one entity instance can be associated with multiple instances of another entity, but each instance of the second entity can only be associated with one instance of the first entity. In this case, one customer can have multiple accounts, but each account can only belong to one customer. 

A clustered index physically reorders the rows in the table based on the index key, which means the rows are stored on disk in the same order as the index. This speeds up retrieval of data based on that index key but may slow down inserts and updates because the rows must be physically reordered. A non-clustered index does not change the physical order of the data on disk and thus doesn't affect insert or update performance, but may be slower for retrieval operations. 

Referential integrity in DB2 ensures data integrity by enforcing relationships between tables. This means that when a foreign key in one table references a primary key in another table, the integrity of the relationship is maintained. For example, if a record in the parent table is deleted or updated, the corresponding records in the child table are also updated or deleted to maintain consistency. This helps prevent orphan records and ensures that the data remains accurate and consistent throughout the database. 

The DB2 Command Line Processor (CLP) is commonly used for basic database administration tasks in DB2. It provides a command-line interface for executing SQL statements, managing database objects, and performing administrative tasks. CLP offers flexibility and efficiency for administrators to interact with the DB2 database system directly from the command line.