A partnership firm is illegal when

Any of the partners is from enemy country
Established for unlimited period
There are seven partners
Registered under the Partnership Act

The correct answer is: A. Any of the partners is from enemy country.

A partnership firm is illegal when any of the partners is from an enemy country. This is because, under the Partnership Act, a partnership firm can only be formed between two or more persons who are natural persons, i.e., human beings. A partnership firm cannot be formed between a natural person and a juristic person, i.e., a legal entity such as a company. An enemy country is a country with which India is at war. Therefore, a partnership firm cannot be formed between a person from India and a person from an enemy country.

The other options are not correct because:

  • A partnership firm can be established for an unlimited period.
  • There is no limit on the number of partners in a partnership firm.
  • A partnership firm is not required to be registered under the Partnership Act. However, it is advisable to register a partnership firm for the sake of convenience and to enjoy certain benefits.