The appropriate method to know the opinion of class X students on a certain issue is through an interview. An interview allows the teacher to directly interact with the students, ask them questions, and gather their opinions and thoughts on the issue at hand. Let's explore this in more detail:

Benefits of an interview:
- Personal Interaction: An interview provides an opportunity for the teacher to have a direct conversation with the students. This allows for a more personal and in-depth understanding of their opinions and perspectives.
- Flexibility: The teacher can ask follow-up questions, probe deeper into certain points, and clarify any doubts during the interview. This flexibility helps in gaining a comprehensive understanding of the students' opinions.
- Gathering Diverse Opinions: An interview allows the teacher to gather opinions from different students in the class. This helps in getting a range of perspectives and a better representation of the overall class opinion.

Procedure for conducting an interview:
1. Plan and Prepare: The teacher should decide on the specific issue or topic for which they want to gather the students' opinions. They should also prepare a set of questions that will help explore different aspects of the issue.
2. Inform the students: The teacher should inform the students in advance about the interview and the purpose behind it. This will help the students prepare their thoughts and opinions.
3. Conduct the interview: The teacher can either conduct individual interviews with each student or group interviews with a small number of students at a time. During the interview, the teacher should ask open-ended questions that encourage the students to express their opinions freely.
4. Active listening: The teacher should actively listen to the students' responses, taking notes if necessary. This will help in capturing their opinions accurately.
5. Summarize and analyze: After completing the interviews, the teacher should summarize the main points and analyze the overall opinion of the class. This will help in understanding the collective viewpoint.

Conclusion:
Conducting interviews with class X students is the most appropriate method for knowing their opinions on a certain issue. It allows for personal interaction, flexibility, and gathering diverse opinions. By following a proper procedure, the teacher can effectively gather and analyze the students' opinions, which can then be used for further discussions or decision-making.