Question 2
What is the unit of momentum, and what kind of quantity is it?
The right answer is the one marked above.
kg m s−1; it is a vector quantity. Momentum = mass × velocity, so the units multiply too: kg × m s−1 = kg m s−1.
Velocity is a vector and mass is a scalar. A vector multiplied by a scalar gives a vector — and its direction is the direction of the velocity.
kg m s−2 is the newton, the unit of force. The only difference is the power of the second, so take care.