Water heater contains 56 part a how many kilowatt-hours of energy are necessary to heat the water in the water heater by 25 ? c?

Answer is: 550,021 kWh of energy is needed to heat the water 

V(water) = 51 gal = 51·3,78 = 189,3 L.

ΔT(water) = 25°C.

d(water) = 1000 g/L.

m(water) = V(water) · d(water)

m(water) = 189,3 L · 1000 g/L

m(water) = 189300 g.

Q = m(water) · ΔT(water) · C(water)

Q = 189300 g · 25°C · 4,184 J/°C·g

Q = 19800780 J = 19800,78 kJ ÷ 3600 = 550,021 kWh.

the answer is d.) potassium