The elements which have similar behavior are Barium, strontium and beryllium.
I think the airplan flies in same speed 400
Answer:1.27
Explanation:
Given
incident angle 
refracted angle 
Suppose
is the refractive index of material then using Snell's law we can write

where
=refractive index of air



Answer:
A
Explanation:
It is less than the acceleration of the backpack because abs has a greater mass.