A non-optional social convention refers to a customary practice or behavior that is expected or required in a particular society or culture. These conventions are not optional and are considered necessary for individuals to adhere to in order to be accepted or respected within that social group. Failure to comply with these conventions may result in social consequences or ostracization. Examples of non-optional social conventions include greeting someone with a handshake or bowing in certain cultures, or following specific dress codes for formal events. **

Optional means that something is not required or mandatory. It is up to the individual's discretion whether to choose or use it. In other words, it is something that can be done or used if desired, but is not necessary. **

Yes, dual citizenship is optional in many countries. Some countries allow individuals to hold citizenship in more than one country, while others do not. It is important to check the laws and regulations of each country to determine if dual citizenship is allowed and what the requirements are for obtaining it. Additionally, some countries may have restrictions on dual citizenship, such as requiring individuals to renounce their citizenship in one country in order to become a citizen of another. **

Wearing a tie is often considered a formal or professional dress code requirement in many settings such as business meetings, interviews, or formal events. However, in more casual or relaxed environments, wearing a tie may be optional. It ultimately depends on the specific dress code of the event or workplace. **

Prison food is not always optional for inmates. In many cases, prisoners are required to eat the meals provided by the prison facility. However, some prisons may offer alternative options for inmates with dietary restrictions or religious dietary requirements. Overall, the availability of optional food choices in prison can vary depending on the specific policies of the facility. **

Second foreign languages should not be optional because learning a new language can provide numerous cognitive and academic benefits, such as improved memory, problem-solving skills, and multitasking abilities. Additionally, in our increasingly globalized world, being proficient in multiple languages can open up more opportunities for personal and professional growth. Making second foreign languages mandatory can also promote cultural understanding and communication across borders. **

An optional phone number means that providing a phone number is not required in order to complete a form or sign up for a service. It gives individuals the choice to include their phone number if they wish, but it is not mandatory. This can be helpful for those who prefer not to share their phone number or for situations where it is not necessary for communication. **

The opposite of optional is mandatory. When something is mandatory, it is required or obligatory, meaning it must be done or used. This is in contrast to something that is optional, which is not required and can be chosen or omitted. **