Instrumental motivation is when :

The correct option is: a person learns the language for utilitarian reason like employment.

Understanding Instrumental Motivation:
In second-language acquisition theory (formulated by socio-psychologists Robert Gardner and Wallace Lambert), motivation to learn a language is broadly divided into two main categories:

1. Instrumental Motivation: This refers to learning a language as a practical tool or "instrument" to achieve pragmatic, functional goals. Examples include getting a job, acquiring a promotion, satisfying a graduation requirement, passing an exam, or translating documents.

2. Integrative Motivation: This refers to learning a language out of a desire to integrate into the target language culture, communicate with native speakers, and participate in their social and cultural community.

Analysis of Options:
- "a person learns the language for utilitarian reason like employment.": This directly aligns with the definition of instrumental motivation, as employment is a practical and utilitarian objective.
- "a person learns the language for being closer to the native speakers of the language.": This describes integrative motivation, not instrumental motivation.
- "a person learns the language for writing a book." or social integration: These lean toward personal/creative fulfillment or socio-cultural integration.

Therefore, learning a language for utilitarian reasons such as securing employment is a classic example of instrumental motivation.