Q = mCpΔT —> Solve for Cp —> Cp = q/mΔT
q = -6700 J (negative because it released heat
m = 70 g
ΔT = Final temp - initial temp = 25 - 90 = -65°C
Cp = -6700 J / (70 g)(-65°C) = 1.47 J/g°C
I think the answer is C. 02
If you have a magnesium for every oxygen, then you have to start with two magnesiums. So the balanced equation is 2 Mg + O2 2 MgO.
And
CaCO3———→CaO + CO2
I hope it helped!
