Valence electrons are required for certain bonding processes. Without them you cannot bond with certain elements. For example, carbon bonds really well with carbon because it has the same amount of valence electrons. However carbon would not bond well with uranium due to the massive differences in valence electrons. Hope this helps!
Transformation of energy, because energy cannot be created or destroyed
Answer:
Q1: (a)

so

Q2:

this is the radius in meter
diameter = 2r
in this i don't know which choice is the right answer
Q3:

so

again there is no correct answer