Answer:
a
The focal length of the lens in water is 
b
The focal length of the mirror in water is 
Explanation:
From the question we are told that
The index of refraction of the lens material = 
The index of refraction of the medium surrounding the lens = 
The lens maker's formula is mathematically represented as
![\frac{1}{f} = (n -1) [\frac{1}{R_1} - \frac{1}{R_2} ]](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7Bf%7D%20%3D%20%28n%20-1%29%20%5B%5Cfrac%7B1%7D%7BR_1%7D%20-%20%5Cfrac%7B1%7D%7BR_2%7D%20%20%5D)
Where
is the focal length
is the index of refraction
are the radius of curvature of sphere 1 and 2 of the lens
From the question When the lens in air we have
![\frac{1}{f_{air}} = (n-1) [\frac{1}{R_1} - \frac{1}{R_2} ]](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7Bf_%7Bair%7D%7D%20%3D%20%28n-1%29%20%5B%5Cfrac%7B1%7D%7BR_1%7D%20-%20%5Cfrac%7B1%7D%7BR_2%7D%20%20%5D)
When immersed in liquid the formula becomes
![\frac{1}{f_{water}} = [\frac{n_2}{n_1} - 1 ] [\frac{1}{R_1} - \frac{1}{R_2} ]](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7Bf_%7Bwater%7D%7D%20%3D%20%5B%5Cfrac%7Bn_2%7D%7Bn_1%7D%20-%201%20%5D%20%5B%5Cfrac%7B1%7D%7BR_1%7D%20-%20%5Cfrac%7B1%7D%7BR_2%7D%20%20%5D)
The ratio of the focal length of the the two medium is mathematically evaluated as
![\frac{f_water}{f_{air}} = \frac{n_2 -1}{[\frac{n_2}{n_1} - 1] }](https://tex.z-dn.net/?f=%5Cfrac%7Bf_water%7D%7Bf_%7Bair%7D%7D%20%3D%20%5Cfrac%7Bn_2%20-1%7D%7B%5B%5Cfrac%7Bn_2%7D%7Bn_1%7D%20-%201%5D%20%7D)
From the question
= 79.0 cm

and the refractive index of water(material surrounding the lens) has a constant value of 


b
The focal length of a mirror is dependent on the concept of reflection which is not affected by medium around it.
The answer would be:
D.
X: Low potential energy
Y: High Potential energy
Z: Flow of electrons
Z is clearly the flow of electrons, as shown by the arrow demonstrating the direction of the flow. So you can easily cross out choices B and C. Now, you can see that Y has more energy stored and X has a lot less, so you can conclude that Y has high potential energy while X has low potential energy.
<span><span>Your hand will be cold.
if you do it often enough, you will realize your fingernails will not grow as fast (Fun fact)
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