<u>Answer:</u> The amount of heat released when 0.211 moles of 
reacts is 554.8 kJ
<u>Explanation:</u>
The chemical equation for the reaction of 
with oxygen gas follows:
The equation for the enthalpy change of the above reaction is:
![\Delta H_{rxn}=[(5\times \Delta H_f_{(B_2O_3(s))})+(9\times \Delta H_f_{(H_2O(l))})]-[(2\times \Delta H_f_{(B_5H_9(l))})+(12\times \Delta H_f_{(O_2(g))})]](https://tex.z-dn.net/?f=%5CDelta%20H_%7Brxn%7D%3D%5B%285%5Ctimes%20%5CDelta%20H_f_%7B%28B_2O_3%28s%29%29%7D%29%2B%289%5Ctimes%20%5CDelta%20H_f_%7B%28H_2O%28l%29%29%7D%29%5D-%5B%282%5Ctimes%20%5CDelta%20H_f_%7B%28B_5H_9%28l%29%29%7D%29%2B%2812%5Ctimes%20%5CDelta%20H_f_%7B%28O_2%28g%29%29%7D%29%5D)
We are given:
Putting values in above equation, we get:
![\Delta H_{rxn}=[(2\times (-1272))+(9\times (-285.4))]-[(2\times (73.2))+(12\times (0))]\\\\\Delta H_{rxn}=-5259kJ](https://tex.z-dn.net/?f=%5CDelta%20H_%7Brxn%7D%3D%5B%282%5Ctimes%20%28-1272%29%29%2B%289%5Ctimes%20%28-285.4%29%29%5D-%5B%282%5Ctimes%20%2873.2%29%29%2B%2812%5Ctimes%20%280%29%29%5D%5C%5C%5C%5C%5CDelta%20H_%7Brxn%7D%3D-5259kJ)
To calculate the amount of heat released for the given amount of , we use unitary method, we get:
When 2 moles of reacts, the amount of heat released is 5259 kJ
So, when 0.211 moles of will react, the amount of heat released will be = 
Hence, the amount of heat released when 0.211 moles of reacts is 554.8 kJ
The atomic number of Fe= 26
The electronic configuration of Fe will be
1s2 2s2 2p6 3s2 3p6 4s2 3d6
When it loses two electrons to form ferrous ion (Fe(II)) the electrons will be loose by 4s orbital first
So the electronic configuration of Fe^+2 ion will be
1s2 2s2 2p6 3s2 3p6 3d6
Hence there are six electrons in 3d orbital of iron dipositive ion
Now the the electrons in 3d orbital will be like:
so there are four unpaired electrons
