(i) The magnitude of a physical quantity is 8.5Ns.Name the physical quantity (ii) Why is it dangerous to jump out of a moving vehicle? How can the danger be minimized?

The physical quantity is momentum.

Ns(Newton second) is the unit of Force x time which is equal to change in momentum.

F = dP/dt

dP = F x t

We can't jump out of moving vehicle because we may fall due to our inertia of motion. (i had an experience of getting my knees bruised when i stepped out of a moving bus before it stopped.).

When you are in bus, u are moving with the velocity of bus with respect to ground. So you have the interia which can be understood as your momentum in this case. So when u jump out of a bus, u change your speed from a finite value to zero instantaneously, which causes an abrupt change in momentum, which your body will try to resist. So your upper body will still be in motion while your feet are still. It means you will definitely fall down. So it is advised not to jump from a moving bus

if you indeed want to jump outside then try to run forward in same direction for some time to gradually decrease your momentum.

Remember F = dP/dt

if you change your momentum in a greater time interval dt, you will experience less impulsive force F.