A reaction that takes place in laboratory rather than in a living body is called

The correct option is In vitro.

In biological and chemical sciences, reactions and processes are often classified based on the environment in which they occur. Let us break down the meaning of the terms to understand why In vitro is the correct choice:

1. In vitro: This is a Latin term that translates literally to "in glass". It refers to biological or chemical studies, reactions, or experiments performed outside of a living organism, typically in laboratory glassware such as test tubes, flasks, or petri dishes. Therefore, any reaction that takes place in a laboratory setting rather than inside a living body is referred to as an in vitro reaction.
2. In situ: This term translates to "on site" or "in position". In biology, it refers to examining or observing a phenomenon exactly where it occurs naturally (e.g., looking at a cell within a whole tissue block) without moving it to a test tube, but it does not specifically denote a reaction taking place in a laboratory.
3. Instant: This is a general term meaning happening immediately or without delay, and is not a scientific classification for the venue of a reaction.
4. In house: This is a business or organizational term referring to work done within a company or institution rather than by external contractors.

Thus, reactions conducted in a laboratory environment outside a living system are scientifically classified as In vitro.