Explanation:

- The Factories Act, 1948 defines an 'Adolescent' as someone who has completed 15 years of age but is less than 18 years.

- Option 1: Who has completed 15 years of age but is less than 18 years.

- This is correct as per the Act. Adolescents are those who are between the ages of 15 and 17.

- Option 2: Who is less than 18 years.

- This definition is too broad and includes children.

- Option 3: Who has completed 14 years of age but is less than 18 years.

- This includes individuals under the age limit for adolescents.

- Option 4: Who has completed 16 years of age but is less than 18 years.

- This excludes adolescents aged 15 to 16.