<u>Answer:</u> The enthalpy of the overall chemical equation is -205.7 kJ
<u>Explanation:</u>
Hess's law is defined as the law which states that the total amount of heat absorbed or released for a given chemical reaction will remain the same whether the process occurs in one step or several steps.
In this law, a chemical equation is treated as an ordinary algebraic expression that can be added or subtracted to yield the required overall equation.
The enthalpy change or heat of the overall reaction is the summation of the enthalpies or heats of the intermediate reactions involved in the process.
The given overall chemical equation follows:

The intermediate equations for the above reaction are:
(1) 
(2) 
(3) 
According to Hess law, the enthalpy of the reaction becomes:
![\Delta H^o_{rxn}=[1\times (\Delta H_1)] + [1\times (-\Delta H_2)] + [2\times (\Delta H_3)]](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5B1%5Ctimes%20%28%5CDelta%20H_1%29%5D%20%2B%20%5B1%5Ctimes%20%28-%5CDelta%20H_2%29%5D%20%2B%20%5B2%5Ctimes%20%28%5CDelta%20H_3%29%5D)
Putting values in above expression, we get:
![\Delta H^o_{rxn}=[1\times (74.6)] + [1\times (-95.7)] + [2\times (-92.3)]\\\\\Delta H^o_{rxn}=-205.7kJ](https://tex.z-dn.net/?f=%5CDelta%20H%5Eo_%7Brxn%7D%3D%5B1%5Ctimes%20%2874.6%29%5D%20%2B%20%5B1%5Ctimes%20%28-95.7%29%5D%20%2B%20%5B2%5Ctimes%20%28-92.3%29%5D%5C%5C%5C%5C%5CDelta%20H%5Eo_%7Brxn%7D%3D-205.7kJ)
Hence, the enthalpy of the overall chemical equation is -205.7 kJ
Answer: -
¹⁰B
Explanation: -
For ⁹Be,
The atomic number is 4.
The Mass number is 9.
The number of neutrons = mass number - atomic number
= 9 - 4 = 5
For ⁹B,
The atomic number is 5.
The Mass number is 9.
The number of neutrons = mass number - atomic number
= 9-5 = 4
For ¹⁰B,
The atomic number is 5.
The Mass number is 10.
The number of neutrons = mass number - atomic number
= 10-5 = 5
For ¹⁰Be,
TThe atomic number is 4.
The Mass number is 10.
The number of neutrons = mass number - atomic number
= 10-4 = 6
For ¹²C,
The atomic number is 6.
The Mass number is 12.
The number of neutrons = mass number - atomic number
= 12-6 = 6
<span>The answer is "D" where the number of collisions per unit area is reduced by one-half. Drawing back on the piston means the volume is increased. The pressure is reduced. There are fewer collisions when the pressure is reduced.</span>