Answer:
C. rollback
Explanation:
The retina of the eye is located inside the eye making it impossible for the retina to roll back. Only the eye itself can rollback.
Answer:
(a) 30 m/sec
(b) -50 m/sec
Explanation:
We have given initial velocity of ball u = 50 m/sec
Acceleration due to gravity 
(a) Time t = 2 sec
Now according to first equation of v = u-gt
So v=50-10×2=30 m/sec
(b) Time t = 10 sec
Now according to first equation of motion
So final velocity v = u-gt = 50-10×10 =-50 m/sec
Yes, N2 is a triple bond.
Hope it helps!