153g/mols I think this is the answer but not 100% sure.
It is a Compound.
Water can't be a mixture because it is chemically bonded and cannot be separated into H2 and O by physical means.
And water cannot be an element, because it is made of atoms of different types [H and Oxygen]
It depends on the type of decay that is taking place if its a β+ it will decay into Mn-52 β- decays into Co-59
Answer: Transition from X to Y will have greater energy difference.
Explanation: For studying the energy difference, we require Planck's equation.

where, h = Planck's Constant
c = Speed of light
E = Energy
= Wavelength of particle
From the equation, it is visible that the energy and wavelength follow inverse relation which means that with low wavelength value, energy will be the highest and vice-versa.
As electron A falls from X-energy level to Y-energy level, it releases blue light which has low wavelength value (around 470 nm) which means that it has high energy.
Similarly, Electron B releases red light when it falls from Y-energy level to Z-energy level, which has high wavelength value (around 700 nm), giving it a low energy value.
Energy Difference between X-energy level and Y-energy level will be more.