The mass number of fe2+ is 56. how many neutrons are there in a single fe2+ atom?

the number of neutrons present in a single   atom is 30

Explanation: Given atom is  which is basically ion of iron from which two electrons have been removed .

Thus Atomic number of , Z = 26

Mass number of  , M=56

Now we know that the mass number of the atom (M) is equal to the sum of the number of protons(P) and neutrons(N) in the nucleus ,i.e., M=P+N ----(A)

Also the number of protons in the nucleus of the atom is equal to the atomic number (Z).

Therefore number of protons , P=Z= 26    

Using equation (A) we get

56=26+ N

=>N=30

Thus the number of neutrons present in a single   atom is 30

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.

need to see circuit to get time constant