The question asks to identify which of the given countries is not a member of the Association of South-East Asian Nations (ASEAN). ASEAN is a significant intergovernmental organization in the Southeast Asian region. Its primary goals include promoting economic growth, social progress, cultural development, and regional peace and stability among its member states.

ASEAN Formation and Purpose

ASEAN was officially established on August 8, 1967, in Bangkok, Thailand, through the signing of the ASEAN Declaration, commonly known as the Bangkok Declaration. The five founding member countries were Indonesia, Malaysia, the Philippines, Singapore, and Thailand. Over the decades, the organization expanded to include all ten countries of Southeast Asia, fostering cooperation across various sectors like trade, security, and culture.

Current ASEAN Member Countries

To determine which country is not an ASEAN member, it's essential to know the current list of states that comprise the Association of South-East Asian Nations. Currently, ASEAN has ten member countries:

• Brunei Darussalam (joined 1984)
• Cambodia (joined 1999)
• Indonesia (founding member, 1967)
• Laos (joined 1997)
• Malaysia (founding member, 1967)
• Myanmar (joined 1997)
• Philippines (founding member, 1967)
• Singapore (founding member, 1967)
• Thailand (founding member, 1967)
• Vietnam (joined 1995)

Analyzing Countries in Options

Let's evaluate each option provided in the question against the list of ASEAN member countries:

• Singapore: Singapore is one of the five founding members of ASEAN, having joined in 1967. Therefore, Singapore is a member.
• Malaysia: Malaysia is also one of the five founding members of ASEAN, having joined in 1967. Therefore, Malaysia is a member.
• Japan: Japan is an East Asian country and is not geographically located in Southeast Asia. While Japan is a crucial "dialogue partner" of ASEAN, engaging in extensive cooperation across economic, political, and cultural fields, it is not a full member state of the organization.
• Cambodia: Cambodia joined ASEAN on April 30, 1999, becoming the tenth member. Therefore, Cambodia is a member.

Conclusion on ASEAN Non-Membership

Based on the membership status, Singapore, Malaysia, and Cambodia are all integral member countries of the Association of South-East Asian Nations (ASEAN). Japan, despite its close ties and significant role as a dialogue partner, is not a member of ASEAN. The organization is exclusively composed of countries from the Southeast Asian region.