Answer: b and c are the same so that leaves you with a and d I believe it's d not sure hope this helps ®:]©™
Explanation:
Refraction. refraction is always accompanied by a wavelength and speed change
Number of electrons transferred: 
Explanation:
The charge on the first object is

while the charge on the 2nd object is

When they are in contact, the final charge on each object will be

So, the amount of charge (electrons) transferred from the 1st object to the 2nd object is

The charge of one electron is

Therefore, the number of electrons transferred is

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Answer:
when the center of gravity is within the washing area, the torque returns in the body to its initial position and is in a stable equilibrium
Explanation:
The concept of center of gravity is equivalent to the concept of center of mass, in this place all external forces applied can be considered.
When we analyze the balance of a body that is the torque it is the one that defines the balance
τ = F xd
If the torque tends to restore the body to the initial position the balance is stable, but if the torque has to increase the body's rotation the balance is unstable
. When the body tends to rotate the torque with respect to the pivot point at the base it decreases because the distance from the center of gravity to the end of the base decreases in value, but it has to return it to the initial position, the balance is stable. The critical point of this process is when the center of gravity is at the limit of the body base area in this case the torque is zero; If the body rotates a little more the center of gravity is outside the base, the torque changes sign and has to increase the turn, going to an unstable balance.
In summary, when the center of gravity is within the washing area, the torque returns in the body to its initial position and is in a stable equilibrium.