Step 1: Understanding the Concept:
Journalistic ethics are the professional standards that guide how news is gathered and told. The main ones are truth, independence, fairness and accountability.
Step 2: Key Approach:
We sort the four options into two groups. One group supports truth and fairness. The other group harms them. The option in the second group is our answer.
Step 3: Options that support the standards.
Crediting sources shows where information came from and keeps the reporter honest. Background checks test whether a claim or person is trustworthy. Verifying facts confirms that a statement is correct before it reaches the public. All three help truth and accountability, so options (1), (2) and (4) are good practice.
Step 4: The option that harms the standards.
Partisan reporting means the report leans towards a political party or interest group. The reporter then picks facts to suit that side and ignores the rest. Readers get a one-sided picture, so fairness and independence are lost.
Step 5: Compare and decide.
Three options protect the reader and one misleads the reader. The misleading practice is the unethical one, which is option (3).
Final Answer:
The unethical practice is partisan reporting, option (3).
\[ \boxed{\text{3}} \]