It's not B so I'm thinking it is D.
Answer : 9773 kJ
Explanation:
Exothermic reactions are defined as the reactions in which energy of the product is lesser than the energy of the reactants. The total energy is released in the form of heat and
for the reaction comes out to be negative.
To calculate the moles :

Given : Change in enthalpy on combustion of 1 mole of methanol = -1278 kJ
According to stoichiometry :
1 mole of methanol produce energy = 1278 kJ
Thus 7.647 moles of methanol produce energy =
Thus 9773 kJ of energy is produced from burning 245.0 g of methanol in excess oxygen
Atomic Mass will be 23 the new magnesium formed will be its isotope of magnesium.
We know that,
In stable condition
Number of electrons = Number of protons
Atomic number represents number of proton .
So, here number of proton is 12
Therefore, number of electron is 12
We know that -
Atomic mass = number of protons +Number of neutron
So if magnesium loses one neutron i.e. new number of neutron is 11
then its atomic mass changes.
New atomic mass will be
Atomic mass = 
Atomic mass = 23
This new element with atomic mass 23 and atomic number 12 is the isotope of magnesium.
To know more about isotopes
brainly.com/question/11291241
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The answer is (2).
Both the proton and the neutron have masses around 1amu.