The force that causes a 1 kg mass to accelerate at a rate of 1 meter per second squared (m/s²) is 1 Newton (N).

Here's why:

* Newton's Second Law of Motion: This law states that the force (F) acting on an object is equal to its mass (m) multiplied by its acceleration (a): F = m * a

* Applying the Law: In this case, we have:

* mass (m) = 1 kg

* acceleration (a) = 1 m/s²

* Calculating the Force: F = 1 kg * 1 m/s² = 1 N

Therefore, a force of 1 Newton is required to accelerate a 1 kg mass at a rate of 1 meter per second squared.