Question

At company X, an Employee may have none or many Dependents. A Dependent may only be in a single Employee's insurance. What is the cardinality of the relationship between Employee and Dependent?

Unary
One-to-Many
One-to-One
Many-to-Many

Answer 1

One to Many. Because as you said Employee may have many Dependents, but a Dependent can be only in a single Employee.